AMDGPU: Handle new atomicrmw metadata for fadd case

This is the most complex atomicrmw support case. Note we don't have
accurate remarks for all of the cases, which I'm planning on fixing
in a later change with more precise wording.

Continue respecting amdgpu-unsafe-fp-atomics until it's eventual removal.
Also seems to fix a few cases not interpreting amdgpu-unsafe-fp-atomics
appropriately aaggressively.

Author: arsenm

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -16054,26 +16054,21 @@ bool SITargetLowering::isKnownNeverNaNForTargetNode(SDValue Op,
                                                             SNaN, Depth);
 }
 
-#if 0
-// FIXME: This should be checked before unsafe fp atomics are enabled
-// Global FP atomic instructions have a hardcoded FP mode and do not support
-// FP32 denormals, and only support v2f16 denormals.
-static bool fpModeMatchesGlobalFPAtomicMode(const AtomicRMWInst *RMW) {
+// On older subtargets, global FP atomic instructions have a hardcoded FP mode
+// and do not support FP32 denormals, and only support v2f16/f64 denormals.
+static bool atomicIgnoresDenormalModeOrFPModeIsFTZ(const AtomicRMWInst *RMW) {
+  if (RMW->hasMetadata("amdgpu.ignore.denormal.mode"))
+    return true;
+
   const fltSemantics &Flt = RMW->getType()->getScalarType()->getFltSemantics();
-  auto DenormMode = RMW->getParent()->getParent()->getDenormalMode(Flt);
-  if (&Flt == &APFloat::IEEEsingle())
-    return DenormMode == DenormalMode::getPreserveSign();
-  return DenormMode == DenormalMode::getIEEE();
-}
-#endif
+  auto DenormMode = RMW->getFunction()->getDenormalMode(Flt);
+  if (DenormMode == DenormalMode::getPreserveSign())
+    return true;
 
-// The amdgpu-unsafe-fp-atomics attribute enables generation of unsafe
-// floating point atomic instructions. May generate more efficient code,
-// but may not respect rounding and denormal modes, and may give incorrect
-// results for certain memory destinations.
-bool unsafeFPAtomicsDisabled(Function *F) {
-  return F->getFnAttribute("amdgpu-unsafe-fp-atomics").getValueAsString() !=
-         "true";
+  // TODO: Remove this.
+  return RMW->getFunction()
+      ->getFnAttribute("amdgpu-unsafe-fp-atomics")
+      .getValueAsBool();
 }
 
 static OptimizationRemark emitAtomicRMWLegalRemark(const AtomicRMWInst *RMW) {
@@ -16202,75 +16197,76 @@ SITargetLowering::shouldExpandAtomicRMWInIR(AtomicRMWInst *RMW) const {
       return AtomicExpansionKind::CmpXChg;
     }
 
-    if (!AMDGPU::isFlatGlobalAddrSpace(AS) &&
-        AS != AMDGPUAS::BUFFER_FAT_POINTER)
-      return AtomicExpansionKind::CmpXChg;
-
-    if (Subtarget->hasGFX940Insts() && (Ty->isFloatTy() || Ty->isDoubleTy()))
-      return AtomicExpansionKind::None;
-
-    if (AS == AMDGPUAS::FLAT_ADDRESS) {
-      // gfx940, gfx12
-      // FIXME: Needs to account for no fine-grained memory
-      if (Subtarget->hasAtomicFlatPkAdd16Insts() && isHalf2OrBFloat2(Ty))
-        return AtomicExpansionKind::None;
-    } else if (AMDGPU::isExtendedGlobalAddrSpace(AS)) {
-      // gfx90a, gfx940, gfx12
-      // FIXME: Needs to account for no fine-grained memory
-      if (Subtarget->hasAtomicBufferGlobalPkAddF16Insts() && isHalf2(Ty))
-        return AtomicExpansionKind::None;
-
-      // gfx940, gfx12
-      // FIXME: Needs to account for no fine-grained memory
-      if (Subtarget->hasAtomicGlobalPkAddBF16Inst() && isBFloat2(Ty))
-        return AtomicExpansionKind::None;
-    } else if (AS == AMDGPUAS::BUFFER_FAT_POINTER) {
-      // gfx90a, gfx940, gfx12
-      // FIXME: Needs to account for no fine-grained memory
-      if (Subtarget->hasAtomicBufferGlobalPkAddF16Insts() && isHalf2(Ty))
-        return AtomicExpansionKind::None;
-
-      // While gfx90a/gfx940 supports v2bf16 for global/flat, it does not for
-      // buffer. gfx12 does have the buffer version.
-      if (Subtarget->hasAtomicBufferPkAddBF16Inst() && isBFloat2(Ty))
-        return AtomicExpansionKind::None;
-    }
-
-    if (unsafeFPAtomicsDisabled(RMW->getFunction()))
+    // LDS atomics respect the denormal mode from the mode register.
+    //
+    // Traditionally f32 global/buffer memory atomics would unconditionally
+    // flush denormals, but newer targets do not flush. f64/f16/bf16 cases never
+    // flush.
+    //
+    // On targets with flat atomic fadd, denormals would flush depending on
+    // whether the target address resides in LDS or global memory. We consider
+    // this flat-maybe-flush as will-flush.
+    if (Ty->isFloatTy() &&
+        !Subtarget->hasMemoryAtomicFaddF32DenormalSupport() &&
+        !atomicIgnoresDenormalModeOrFPModeIsFTZ(RMW))
       return AtomicExpansionKind::CmpXChg;
 
-    // Always expand system scope fp atomics.
-    if (HasSystemScope)
-      return AtomicExpansionKind::CmpXChg;
+    // FIXME: These ReportUnsafeHWInsts are imprecise. Some of these cases are
+    // safe. The message phrasing also should be better.
+    if (globalMemoryFPAtomicIsLegal(*Subtarget, RMW, HasSystemScope)) {
+      if (AS == AMDGPUAS::FLAT_ADDRESS) {
+        // gfx940, gfx12
+        if (Subtarget->hasAtomicFlatPkAdd16Insts() && isHalf2OrBFloat2(Ty))
+          return ReportUnsafeHWInst(AtomicExpansionKind::None);
+      } else if (AMDGPU::isExtendedGlobalAddrSpace(AS)) {
+        // gfx90a, gfx940, gfx12
+        if (Subtarget->hasAtomicBufferGlobalPkAddF16Insts() && isHalf2(Ty))
+          return ReportUnsafeHWInst(AtomicExpansionKind::None);
 
-    // global and flat atomic fadd f64: gfx90a, gfx940.
-    if (Subtarget->hasFlatBufferGlobalAtomicFaddF64Inst() && Ty->isDoubleTy())
-      return ReportUnsafeHWInst(AtomicExpansionKind::None);
+        // gfx940, gfx12
+        if (Subtarget->hasAtomicGlobalPkAddBF16Inst() && isBFloat2(Ty))
+          return ReportUnsafeHWInst(AtomicExpansionKind::None);
+      } else if (AS == AMDGPUAS::BUFFER_FAT_POINTER) {
+        // gfx90a, gfx940, gfx12
+        if (Subtarget->hasAtomicBufferGlobalPkAddF16Insts() && isHalf2(Ty))
+          return ReportUnsafeHWInst(AtomicExpansionKind::None);
 
-    if (AS != AMDGPUAS::FLAT_ADDRESS && Ty->isFloatTy()) {
-      // global/buffer atomic fadd f32 no-rtn: gfx908, gfx90a, gfx940, gfx11+.
-      if (RMW->use_empty() && Subtarget->hasAtomicFaddNoRtnInsts())
-        return ReportUnsafeHWInst(AtomicExpansionKind::None);
-      // global/buffer atomic fadd f32 rtn: gfx90a, gfx940, gfx11+.
-      if (!RMW->use_empty() && Subtarget->hasAtomicFaddRtnInsts())
-        return ReportUnsafeHWInst(AtomicExpansionKind::None);
-    }
+        // While gfx90a/gfx940 supports v2bf16 for global/flat, it does not for
+        // buffer. gfx12 does have the buffer version.
+        if (Subtarget->hasAtomicBufferPkAddBF16Inst() && isBFloat2(Ty))
+          return ReportUnsafeHWInst(AtomicExpansionKind::None);
+      }
 
-    // flat atomic fadd f32: gfx940, gfx11+.
-    if (AS == AMDGPUAS::FLAT_ADDRESS && Ty->isFloatTy()) {
-      if (Subtarget->hasFlatAtomicFaddF32Inst())
+      // global and flat atomic fadd f64: gfx90a, gfx940.
+      if (Subtarget->hasFlatBufferGlobalAtomicFaddF64Inst() && Ty->isDoubleTy())
         return ReportUnsafeHWInst(AtomicExpansionKind::None);
 
-      // If it is in flat address space, and the type is float, we will try to
-      // expand it, if the target supports global and lds atomic fadd. The
-      // reason we need that is, in the expansion, we emit the check of address
-      // space. If it is in global address space, we emit the global atomic
-      // fadd; if it is in shared address space, we emit the LDS atomic fadd.
-      if (Subtarget->hasLDSFPAtomicAddF32()) {
+      if (AS != AMDGPUAS::FLAT_ADDRESS && Ty->isFloatTy()) {
+        // global/buffer atomic fadd f32 no-rtn: gfx908, gfx90a, gfx940, gfx11+.
         if (RMW->use_empty() && Subtarget->hasAtomicFaddNoRtnInsts())
-          return AtomicExpansionKind::Expand;
+          return ReportUnsafeHWInst(AtomicExpansionKind::None);
+        // global/buffer atomic fadd f32 rtn: gfx90a, gfx940, gfx11+.
         if (!RMW->use_empty() && Subtarget->hasAtomicFaddRtnInsts())
-          return AtomicExpansionKind::Expand;
+          return ReportUnsafeHWInst(AtomicExpansionKind::None);
+      }
+
+      // flat atomic fadd f32: gfx940, gfx11+.
+      if (AS == AMDGPUAS::FLAT_ADDRESS && Ty->isFloatTy()) {
+        if (Subtarget->hasFlatAtomicFaddF32Inst())
+          return ReportUnsafeHWInst(AtomicExpansionKind::None);
+
+        // If it is in flat address space, and the type is float, we will try to
+        // expand it, if the target supports global and lds atomic fadd. The
+        // reason we need that is, in the expansion, we emit the check of
+        // address space. If it is in global address space, we emit the global
+        // atomic fadd; if it is in shared address space, we emit the LDS atomic
+        // fadd.
+        if (Subtarget->hasLDSFPAtomicAddF32()) {
+          if (RMW->use_empty() && Subtarget->hasAtomicFaddNoRtnInsts())
+            return AtomicExpansionKind::Expand;
+          if (!RMW->use_empty() && Subtarget->hasAtomicFaddRtnInsts())
+            return AtomicExpansionKind::Expand;
+        }
       }
     }
 

llvm/test/CodeGen/AMDGPU/GlobalISel/flat-atomic-fadd.f32.ll

@@ -57,7 +57,7 @@ define amdgpu_ps float @flat_atomic_fadd_f32_rtn_intrinsic(ptr %ptr, float %data
   ret float %ret
 }
 
-define amdgpu_ps void @flat_atomic_fadd_f32_no_rtn_atomicrmw(ptr %ptr, float %data) #0 {
+define amdgpu_ps void @flat_atomic_fadd_f32_no_rtn_atomicrmw(ptr %ptr, float %data) {
   ; GFX940-LABEL: name: flat_atomic_fadd_f32_no_rtn_atomicrmw
   ; GFX940: bb.1 (%ir-block.0):
   ; GFX940-NEXT:   liveins: $vgpr0, $vgpr1, $vgpr2
@@ -79,11 +79,11 @@ define amdgpu_ps void @flat_atomic_fadd_f32_no_rtn_atomicrmw(ptr %ptr, float %da
   ; GFX11-NEXT:   [[COPY2:%[0-9]+]]:vgpr_32 = COPY $vgpr2
   ; GFX11-NEXT:   FLAT_ATOMIC_ADD_F32 [[REG_SEQUENCE]], [[COPY2]], 0, 0, implicit $exec, implicit $flat_scr :: (load store syncscope("wavefront") monotonic (s32) on %ir.ptr)
   ; GFX11-NEXT:   S_ENDPGM 0
-  %ret = atomicrmw fadd ptr %ptr, float %data syncscope("wavefront") monotonic
+  %ret = atomicrmw fadd ptr %ptr, float %data syncscope("wavefront") monotonic, !amdgpu.no.fine.grained.memory !0
   ret void
 }
 
-define amdgpu_ps float @flat_atomic_fadd_f32_rtn_atomicrmw(ptr %ptr, float %data) #0 {
+define amdgpu_ps float @flat_atomic_fadd_f32_rtn_atomicrmw(ptr %ptr, float %data) {
   ; GFX940-LABEL: name: flat_atomic_fadd_f32_rtn_atomicrmw
   ; GFX940: bb.1 (%ir-block.0):
   ; GFX940-NEXT:   liveins: $vgpr0, $vgpr1, $vgpr2
@@ -107,10 +107,10 @@ define amdgpu_ps float @flat_atomic_fadd_f32_rtn_atomicrmw(ptr %ptr, float %data
   ; GFX11-NEXT:   [[FLAT_ATOMIC_ADD_F32_RTN:%[0-9]+]]:vgpr_32 = FLAT_ATOMIC_ADD_F32_RTN [[REG_SEQUENCE]], [[COPY2]], 0, 1, implicit $exec, implicit $flat_scr :: (load store syncscope("wavefront") monotonic (s32) on %ir.ptr)
   ; GFX11-NEXT:   $vgpr0 = COPY [[FLAT_ATOMIC_ADD_F32_RTN]]
   ; GFX11-NEXT:   SI_RETURN_TO_EPILOG implicit $vgpr0
-  %ret = atomicrmw fadd ptr %ptr, float %data syncscope("wavefront") monotonic
+  %ret = atomicrmw fadd ptr %ptr, float %data syncscope("wavefront") monotonic, !amdgpu.no.fine.grained.memory !0
   ret float %ret
 }
 
 declare float @llvm.amdgcn.flat.atomic.fadd.f32.p1.f32(ptr, float)
 
-attributes #0 = {"amdgpu-unsafe-fp-atomics"="true" }
+!0 = !{}

llvm/test/CodeGen/AMDGPU/GlobalISel/flat-atomic-fadd.f64.ll

@@ -42,7 +42,7 @@ define amdgpu_ps double @flat_atomic_fadd_f64_rtn_intrinsic(ptr %ptr, double %da
   ret double %ret
 }
 
-define amdgpu_ps void @flat_atomic_fadd_f64_no_rtn_atomicrmw(ptr %ptr, double %data) #0 {
+define amdgpu_ps void @flat_atomic_fadd_f64_no_rtn_atomicrmw(ptr %ptr, double %data) {
   ; GFX90A_GFX940-LABEL: name: flat_atomic_fadd_f64_no_rtn_atomicrmw
   ; GFX90A_GFX940: bb.1 (%ir-block.0):
   ; GFX90A_GFX940-NEXT:   liveins: $vgpr0, $vgpr1, $vgpr2, $vgpr3
@@ -55,11 +55,11 @@ define amdgpu_ps void @flat_atomic_fadd_f64_no_rtn_atomicrmw(ptr %ptr, double %d
   ; GFX90A_GFX940-NEXT:   [[REG_SEQUENCE1:%[0-9]+]]:vreg_64_align2 = REG_SEQUENCE [[COPY2]], %subreg.sub0, [[COPY3]], %subreg.sub1
   ; GFX90A_GFX940-NEXT:   FLAT_ATOMIC_ADD_F64 [[REG_SEQUENCE]], [[REG_SEQUENCE1]], 0, 0, implicit $exec, implicit $flat_scr :: (load store syncscope("wavefront") monotonic (s64) on %ir.ptr)
   ; GFX90A_GFX940-NEXT:   S_ENDPGM 0
-  %ret = atomicrmw fadd ptr %ptr, double %data syncscope("wavefront") monotonic
+  %ret = atomicrmw fadd ptr %ptr, double %data syncscope("wavefront") monotonic, !amdgpu.no.fine.grained.memory !0
   ret void
 }
 
-define amdgpu_ps double @flat_atomic_fadd_f64_rtn_atomicrmw(ptr %ptr, double %data) #0 {
+define amdgpu_ps double @flat_atomic_fadd_f64_rtn_atomicrmw(ptr %ptr, double %data) {
   ; GFX90A_GFX940-LABEL: name: flat_atomic_fadd_f64_rtn_atomicrmw
   ; GFX90A_GFX940: bb.1 (%ir-block.0):
   ; GFX90A_GFX940-NEXT:   liveins: $vgpr0, $vgpr1, $vgpr2, $vgpr3
@@ -78,10 +78,10 @@ define amdgpu_ps double @flat_atomic_fadd_f64_rtn_atomicrmw(ptr %ptr, double %da
   ; GFX90A_GFX940-NEXT:   [[V_READFIRSTLANE_B32_1:%[0-9]+]]:sreg_32 = V_READFIRSTLANE_B32 [[COPY5]], implicit $exec
   ; GFX90A_GFX940-NEXT:   $sgpr1 = COPY [[V_READFIRSTLANE_B32_1]]
   ; GFX90A_GFX940-NEXT:   SI_RETURN_TO_EPILOG implicit $sgpr0, implicit $sgpr1
-  %ret = atomicrmw fadd ptr %ptr, double %data syncscope("wavefront") monotonic
+  %ret = atomicrmw fadd ptr %ptr, double %data syncscope("wavefront") monotonic, !amdgpu.no.fine.grained.memory !0
   ret double %ret
 }
 
 declare double @llvm.amdgcn.flat.atomic.fadd.f64.p1.f64(ptr, double)
 
-attributes #0 = {"amdgpu-unsafe-fp-atomics"="true" }
+!0 = !{}

llvm/test/CodeGen/AMDGPU/GlobalISel/fp-atomics-gfx940.ll

@@ -34,7 +34,7 @@ define amdgpu_kernel void @flat_atomic_fadd_f32_noret_pat(ptr %ptr) {
 ; GFX940-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
 ; GFX940-NEXT:    buffer_inv sc0 sc1
 ; GFX940-NEXT:    s_endpgm
-  %ret = atomicrmw fadd ptr %ptr, float 4.0 seq_cst
+  %ret = atomicrmw fadd ptr %ptr, float 4.0 seq_cst, !amdgpu.no.remote.memory !0
   ret void
 }
 
@@ -50,7 +50,7 @@ define amdgpu_kernel void @flat_atomic_fadd_f32_noret_pat_ieee(ptr %ptr) #0 {
 ; GFX940-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
 ; GFX940-NEXT:    buffer_inv sc0 sc1
 ; GFX940-NEXT:    s_endpgm
-  %ret = atomicrmw fadd ptr %ptr, float 4.0 seq_cst
+  %ret = atomicrmw fadd ptr %ptr, float 4.0 seq_cst, !amdgpu.no.remote.memory !0
   ret void
 }
 
@@ -75,7 +75,7 @@ define float @flat_atomic_fadd_f32_rtn_pat(ptr %ptr, float %data) {
 ; GFX940-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
 ; GFX940-NEXT:    buffer_inv sc0 sc1
 ; GFX940-NEXT:    s_setpc_b64 s[30:31]
-  %ret = atomicrmw fadd ptr %ptr, float 4.0 seq_cst
+  %ret = atomicrmw fadd ptr %ptr, float 4.0 seq_cst, !amdgpu.no.remote.memory !0
   ret float %ret
 }
 
@@ -235,3 +235,5 @@ define void @flat_atomic_fadd_noret_v2f16_agent_offset(ptr %ptr, <2 x half> %val
 }
 
 attributes #0 = { "denormal-fp-math-f32"="ieee,ieee" }
+
+!0 = !{}