[WebAssembly] Change half to use soft promotion rather than PromoteFloat

The default `half` legalization, which Wasm currently uses, does not
respect IEEE conventions: for example, casting to bits may invoke a
lossy libcall, meaning soft float operations cannot be correctly
implemented. Change to the soft promotion legalization which passes
`f16` as an `i16` and treats each `half` operation as an individual
f16->f32->libcall->f32->f16 sequence.

Of note in the test updates are that `from_bits` and `to_bits` are now
libcall-free, and that chained operations now round back to `f16` after
each step.

Fixes the wasm portion of #97981
Fixes the wasm portion of #97975
Fixes: #96438
Fixes: #96438

Author: tgross35

llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h

@@ -40,6 +40,8 @@ class WebAssemblyTargetLowering final : public TargetLowering {
   MVT getPointerTy(const DataLayout &DL, uint32_t AS = 0) const override;
   MVT getPointerMemTy(const DataLayout &DL, uint32_t AS = 0) const override;
 
+  bool softPromoteHalfType() const override { return true; }
+
 private:
   /// Keep a pointer to the WebAssemblySubtarget around so that we can make the
   /// right decision when generating code for different targets.

llvm/test/CodeGen/WebAssembly/f16.ll

@@ -10,25 +10,23 @@ target triple = "wasm32-unknown-unknown"
 
 define void @store(half %x, ptr %p) nounwind {
 ; ALL-LABEL: store:
-; ALL:         .functype store (f32, i32) -> ()
+; ALL:         .functype store (i32, i32) -> ()
 ; ALL-NEXT:  # %bb.0:
-; ALL-NEXT:    local.get $push2=, 1
-; ALL-NEXT:    local.get $push1=, 0
-; ALL-NEXT:    call $push0=, __truncsfhf2, $pop1
-; ALL-NEXT:    i32.store16 0($pop2), $pop0
+; ALL-NEXT:    local.get $push1=, 1
+; ALL-NEXT:    local.get $push0=, 0
+; ALL-NEXT:    i32.store16 0($pop1), $pop0
 ; ALL-NEXT:    return
   store half %x, ptr %p
   ret void
 }
 
 define half @return(ptr %p) nounwind {
 ; ALL-LABEL: return:
-; ALL:         .functype return (i32) -> (f32)
+; ALL:         .functype return (i32) -> (i32)
 ; ALL-NEXT:  # %bb.0:
-; ALL-NEXT:    local.get $push2=, 0
-; ALL-NEXT:    i32.load16_u $push0=, 0($pop2)
-; ALL-NEXT:    call $push1=, __extendhfsf2, $pop0
-; ALL-NEXT:    return $pop1
+; ALL-NEXT:    local.get $push1=, 0
+; ALL-NEXT:    i32.load16_u $push0=, 0($pop1)
+; ALL-NEXT:    return $pop0
   %r = load half, ptr %p
   ret half %r
 }
@@ -80,50 +78,28 @@ define dso_local float @loadf(ptr nocapture readonly %a) local_unnamed_addr noun
 }
 
 define dso_local void @stored(ptr nocapture %a, double %b) local_unnamed_addr nounwind {
-; DEFISEL-LABEL: stored:
-; DEFISEL:         .functype stored (i32, f64) -> ()
-; DEFISEL-NEXT:  # %bb.0:
-; DEFISEL-NEXT:    local.get $push2=, 0
-; DEFISEL-NEXT:    local.get $push1=, 1
-; DEFISEL-NEXT:    call $push0=, __truncdfhf2, $pop1
-; DEFISEL-NEXT:    i32.store16 0($pop2), $pop0
-; DEFISEL-NEXT:    return
-;
-; FASTISEL-LABEL: stored:
-; FASTISEL:         .functype stored (i32, f64) -> ()
-; FASTISEL-NEXT:  # %bb.0:
-; FASTISEL-NEXT:    local.get $push4=, 0
-; FASTISEL-NEXT:    local.get $push3=, 1
-; FASTISEL-NEXT:    call $push2=, __truncdfhf2, $pop3
-; FASTISEL-NEXT:    i32.const $push1=, 65535
-; FASTISEL-NEXT:    i32.and $push0=, $pop2, $pop1
-; FASTISEL-NEXT:    i32.store16 0($pop4), $pop0
-; FASTISEL-NEXT:    return
+; ALL-LABEL: stored:
+; ALL:         .functype stored (i32, f64) -> ()
+; ALL-NEXT:  # %bb.0:
+; ALL-NEXT:    local.get $push2=, 0
+; ALL-NEXT:    local.get $push1=, 1
+; ALL-NEXT:    call $push0=, __truncdfhf2, $pop1
+; ALL-NEXT:    i32.store16 0($pop2), $pop0
+; ALL-NEXT:    return
   %x = tail call i16 @llvm.convert.to.fp16.f64(double %b)
   store i16 %x, ptr %a, align 2
   ret void
 }
 
 define dso_local void @storef(ptr nocapture %a, float %b) local_unnamed_addr nounwind {
-; DEFISEL-LABEL: storef:
-; DEFISEL:         .functype storef (i32, f32) -> ()
-; DEFISEL-NEXT:  # %bb.0:
-; DEFISEL-NEXT:    local.get $push2=, 0
-; DEFISEL-NEXT:    local.get $push1=, 1
-; DEFISEL-NEXT:    call $push0=, __truncsfhf2, $pop1
-; DEFISEL-NEXT:    i32.store16 0($pop2), $pop0
-; DEFISEL-NEXT:    return
-;
-; FASTISEL-LABEL: storef:
-; FASTISEL:         .functype storef (i32, f32) -> ()
-; FASTISEL-NEXT:  # %bb.0:
-; FASTISEL-NEXT:    local.get $push4=, 0
-; FASTISEL-NEXT:    local.get $push3=, 1
-; FASTISEL-NEXT:    call $push2=, __truncsfhf2, $pop3
-; FASTISEL-NEXT:    i32.const $push1=, 65535
-; FASTISEL-NEXT:    i32.and $push0=, $pop2, $pop1
-; FASTISEL-NEXT:    i32.store16 0($pop4), $pop0
-; FASTISEL-NEXT:    return
+; ALL-LABEL: storef:
+; ALL:         .functype storef (i32, f32) -> ()
+; ALL-NEXT:  # %bb.0:
+; ALL-NEXT:    local.get $push2=, 0
+; ALL-NEXT:    local.get $push1=, 1
+; ALL-NEXT:    call $push0=, __truncsfhf2, $pop1
+; ALL-NEXT:    i32.store16 0($pop2), $pop0
+; ALL-NEXT:    return
   %x = tail call i16 @llvm.convert.to.fp16.f32(float %b)
   store i16 %x, ptr %a, align 2
   ret void
@@ -170,33 +146,20 @@ define void @test_bitcast_to_half(ptr %addr, i16 %in) nounwind {
 
 define half @from_bits(i16 %x) nounwind {
 ; ALL-LABEL: from_bits:
-; ALL:         .functype from_bits (i32) -> (f32)
+; ALL:         .functype from_bits (i32) -> (i32)
 ; ALL-NEXT:  # %bb.0:
-; ALL-NEXT:    local.get $push1=, 0
-; ALL-NEXT:    call $push0=, __extendhfsf2, $pop1
+; ALL-NEXT:    local.get $push0=, 0
 ; ALL-NEXT:    return $pop0
   %res = bitcast i16 %x to half
   ret half %res
 }
 
 define i16 @to_bits(half %x) nounwind {
-; DEFISEL-LABEL: to_bits:
-; DEFISEL:         .functype to_bits (f32) -> (i32)
-; DEFISEL-NEXT:  # %bb.0:
-; DEFISEL-NEXT:    local.get $push3=, 0
-; DEFISEL-NEXT:    call $push1=, __truncsfhf2, $pop3
-; DEFISEL-NEXT:    i32.const $push0=, 65535
-; DEFISEL-NEXT:    i32.and $push2=, $pop1, $pop0
-; DEFISEL-NEXT:    return $pop2
-;
-; FASTISEL-LABEL: to_bits:
-; FASTISEL:         .functype to_bits (f32) -> (i32)
-; FASTISEL-NEXT:  # %bb.0:
-; FASTISEL-NEXT:    local.get $push3=, 0
-; FASTISEL-NEXT:    call $push2=, __truncsfhf2, $pop3
-; FASTISEL-NEXT:    i32.const $push1=, 65535
-; FASTISEL-NEXT:    i32.and $push0=, $pop2, $pop1
-; FASTISEL-NEXT:    return $pop0
+; ALL-LABEL: to_bits:
+; ALL:         .functype to_bits (i32) -> (i32)
+; ALL-NEXT:  # %bb.0:
+; ALL-NEXT:    local.get $push0=, 0
+; ALL-NEXT:    return $pop0
     %res = bitcast half %x to i16
     ret i16 %res
 }
@@ -559,27 +522,35 @@ define float @test_sitofp_fadd_i32(i32 %a, ptr %b) nounwind {
 ; DEFISEL-LABEL: test_sitofp_fadd_i32:
 ; DEFISEL:         .functype test_sitofp_fadd_i32 (i32, i32) -> (f32)
 ; DEFISEL-NEXT:  # %bb.0:
-; DEFISEL-NEXT:    local.get $push6=, 1
-; DEFISEL-NEXT:    i32.load16_u $push1=, 0($pop6)
+; DEFISEL-NEXT:    local.get $push8=, 1
+; DEFISEL-NEXT:    i32.load16_u $push7=, 0($pop8)
+; DEFISEL-NEXT:    local.set 1, $pop7
+; DEFISEL-NEXT:    local.get $push9=, 0
+; DEFISEL-NEXT:    f32.convert_i32_s $push0=, $pop9
+; DEFISEL-NEXT:    call $push1=, __truncsfhf2, $pop0
 ; DEFISEL-NEXT:    call $push2=, __extendhfsf2, $pop1
-; DEFISEL-NEXT:    local.get $push7=, 0
-; DEFISEL-NEXT:    f32.convert_i32_s $push0=, $pop7
-; DEFISEL-NEXT:    call $push3=, __truncsfhf2, $pop0
-; DEFISEL-NEXT:    call $push4=, __extendhfsf2, $pop3
-; DEFISEL-NEXT:    f32.add $push5=, $pop2, $pop4
-; DEFISEL-NEXT:    return $pop5
+; DEFISEL-NEXT:    local.get $push10=, 1
+; DEFISEL-NEXT:    call $push3=, __extendhfsf2, $pop10
+; DEFISEL-NEXT:    f32.add $push4=, $pop2, $pop3
+; DEFISEL-NEXT:    call $push5=, __truncsfhf2, $pop4
+; DEFISEL-NEXT:    call $push6=, __extendhfsf2, $pop5
+; DEFISEL-NEXT:    return $pop6
 ;
 ; FASTISEL-LABEL: test_sitofp_fadd_i32:
 ; FASTISEL:         .functype test_sitofp_fadd_i32 (i32, i32) -> (f32)
 ; FASTISEL-NEXT:  # %bb.0:
-; FASTISEL-NEXT:    local.get $push6=, 1
-; FASTISEL-NEXT:    i32.load16_u $push2=, 0($pop6)
+; FASTISEL-NEXT:    local.get $push8=, 1
+; FASTISEL-NEXT:    i32.load16_u $push7=, 0($pop8)
+; FASTISEL-NEXT:    local.set 1, $pop7
+; FASTISEL-NEXT:    local.get $push9=, 0
+; FASTISEL-NEXT:    f32.convert_i32_s $push1=, $pop9
+; FASTISEL-NEXT:    call $push2=, __truncsfhf2, $pop1
 ; FASTISEL-NEXT:    call $push3=, __extendhfsf2, $pop2
-; FASTISEL-NEXT:    local.get $push7=, 0
-; FASTISEL-NEXT:    f32.convert_i32_s $push1=, $pop7
-; FASTISEL-NEXT:    call $push4=, __truncsfhf2, $pop1
-; FASTISEL-NEXT:    call $push5=, __extendhfsf2, $pop4
-; FASTISEL-NEXT:    f32.add $push0=, $pop3, $pop5
+; FASTISEL-NEXT:    local.get $push10=, 1
+; FASTISEL-NEXT:    call $push4=, __extendhfsf2, $pop10
+; FASTISEL-NEXT:    f32.add $push5=, $pop3, $pop4
+; FASTISEL-NEXT:    call $push6=, __truncsfhf2, $pop5
+; FASTISEL-NEXT:    call $push0=, __extendhfsf2, $pop6
 ; FASTISEL-NEXT:    return $pop0
   %tmp0 = load half, ptr %b
   %tmp1 = sitofp i32 %a to half
@@ -590,17 +561,20 @@ define float @test_sitofp_fadd_i32(i32 %a, ptr %b) nounwind {
 
 define half @chained_fp_ops(half %x) {
 ; ALL-LABEL: chained_fp_ops:
-; ALL:         .functype chained_fp_ops (f32) -> (f32)
+; ALL:         .functype chained_fp_ops (i32) -> (i32)
+; ALL-NEXT:    .local f32
 ; ALL-NEXT:  # %bb.0: # %start
-; ALL-NEXT:    local.get $push6=, 0
-; ALL-NEXT:    call $push0=, __truncsfhf2, $pop6
-; ALL-NEXT:    call $push5=, __extendhfsf2, $pop0
-; ALL-NEXT:    local.tee $push4=, 0, $pop5
-; ALL-NEXT:    local.get $push7=, 0
-; ALL-NEXT:    f32.add $push1=, $pop4, $pop7
-; ALL-NEXT:    f32.const $push2=, 0x1p-1
-; ALL-NEXT:    f32.mul $push3=, $pop1, $pop2
-; ALL-NEXT:    return $pop3
+; ALL-NEXT:    local.get $push8=, 0
+; ALL-NEXT:    call $push7=, __extendhfsf2, $pop8
+; ALL-NEXT:    local.tee $push6=, 1, $pop7
+; ALL-NEXT:    local.get $push9=, 1
+; ALL-NEXT:    f32.add $push0=, $pop6, $pop9
+; ALL-NEXT:    call $push2=, __truncsfhf2, $pop0
+; ALL-NEXT:    call $push3=, __extendhfsf2, $pop2
+; ALL-NEXT:    f32.const $push1=, 0x1p-1
+; ALL-NEXT:    f32.mul $push4=, $pop3, $pop1
+; ALL-NEXT:    call $push5=, __truncsfhf2, $pop4
+; ALL-NEXT:    return $pop5
 start:
   %y = fmul half %x, 0xH4000
   %z = fdiv half %y, 0xH4000
@@ -609,16 +583,15 @@ start:
 
 define half @test_select_cc(half) nounwind {
 ; ALL-LABEL: test_select_cc:
-; ALL:         .functype test_select_cc (f32) -> (f32)
+; ALL:         .functype test_select_cc (i32) -> (i32)
 ; ALL-NEXT:  # %bb.0:
-; ALL-NEXT:    f32.const $push4=, 0x1p0
+; ALL-NEXT:    i32.const $push4=, 15360
+; ALL-NEXT:    i32.const $push3=, 0
+; ALL-NEXT:    local.get $push6=, 0
+; ALL-NEXT:    call $push1=, __extendhfsf2, $pop6
 ; ALL-NEXT:    f32.const $push0=, 0x0p0
-; ALL-NEXT:    local.get $push7=, 0
-; ALL-NEXT:    call $push1=, __truncsfhf2, $pop7
-; ALL-NEXT:    call $push2=, __extendhfsf2, $pop1
-; ALL-NEXT:    f32.const $push6=, 0x0p0
-; ALL-NEXT:    f32.ne $push3=, $pop2, $pop6
-; ALL-NEXT:    f32.select $push5=, $pop4, $pop0, $pop3
+; ALL-NEXT:    f32.ne $push2=, $pop1, $pop0
+; ALL-NEXT:    i32.select $push5=, $pop4, $pop3, $pop2
 ; ALL-NEXT:    return $pop5
   %2 = fcmp une half %0, 0xH0000
   %3 = uitofp i1 %2 to half
@@ -627,27 +600,28 @@ define half @test_select_cc(half) nounwind {
 
 define half @fabs(half %x) nounwind {
 ; ALL-LABEL: fabs:
-; ALL:         .functype fabs (f32) -> (f32)
+; ALL:         .functype fabs (i32) -> (i32)
 ; ALL-NEXT:  # %bb.0:
-; ALL-NEXT:    local.get $push3=, 0
-; ALL-NEXT:    call $push0=, __truncsfhf2, $pop3
-; ALL-NEXT:    call $push1=, __extendhfsf2, $pop0
-; ALL-NEXT:    f32.abs $push2=, $pop1
-; ALL-NEXT:    return $pop2
+; ALL-NEXT:    local.get $push2=, 0
+; ALL-NEXT:    i32.const $push0=, 32767
+; ALL-NEXT:    i32.and $push1=, $pop2, $pop0
+; ALL-NEXT:    return $pop1
   %a = call half @llvm.fabs.f16(half %x)
   ret half %a
 }
 
 define half @fcopysign(half %x, half %y) nounwind {
 ; ALL-LABEL: fcopysign:
-; ALL:         .functype fcopysign (f32, f32) -> (f32)
+; ALL:         .functype fcopysign (i32, i32) -> (i32)
 ; ALL-NEXT:  # %bb.0:
-; ALL-NEXT:    local.get $push3=, 0
-; ALL-NEXT:    call $push0=, __truncsfhf2, $pop3
-; ALL-NEXT:    call $push1=, __extendhfsf2, $pop0
-; ALL-NEXT:    local.get $push4=, 1
-; ALL-NEXT:    f32.copysign $push2=, $pop1, $pop4
-; ALL-NEXT:    return $pop2
+; ALL-NEXT:    local.get $push5=, 0
+; ALL-NEXT:    i32.const $push2=, 32767
+; ALL-NEXT:    i32.and $push3=, $pop5, $pop2
+; ALL-NEXT:    local.get $push6=, 1
+; ALL-NEXT:    i32.const $push0=, -32768
+; ALL-NEXT:    i32.and $push1=, $pop6, $pop0
+; ALL-NEXT:    i32.or $push4=, $pop3, $pop1
+; ALL-NEXT:    return $pop4
   %a = call half @llvm.copysign.f16(half %x, half %y)
   ret half %a
 }