[InstSimplify] Simplify fcmp implied by dominating fcmp (llvm#161090)

dtcxzyw · web-flow · commit ca5ece89394f · 2025-10-05T16:15:51.000+08:00
This patch simplifies an fcmp into true/false if it is implied by a dominating fcmp. As an initial support, it only handles two cases: + `fcmp pred1, X, Y -> fcmp pred2, X, Y`: use set operations. + `fcmp pred1, X, C1 -> fcmp pred2, X, C2`: use `ConstantFPRange` and set operations. Note: It doesn't fix llvm#70985, as the second fcmp in the motivating case is not dominated by the edge. We may need to adjust JumpThreading to handle this case. Comptime impact (~+0.1%): https://llvm-compile-time-tracker.com/compare.php?from=a728f213c863e4dd19f8969a417148d2951323c0&to=8ca70404fb0d66a824f39d83050ac38e2f1b25b9&stat=instructions:u IR diff: dtcxzyw/llvm-opt-benchmark#2848
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4164,6 +4164,10 @@ static Value *simplifyFCmpInst(CmpPredicate Pred, Value *LHS, Value *RHS,
       return ConstantInt::get(RetTy, Pred == CmpInst::FCMP_UNO);
   }
 
+  if (std::optional<bool> Res =
+          isImpliedByDomCondition(Pred, LHS, RHS, Q.CxtI, Q.DL))
+    return ConstantInt::getBool(RetTy, *Res);
+
   const APFloat *C = nullptr;
   match(RHS, m_APFloatAllowPoison(C));
   std::optional<KnownFPClass> FullKnownClassLHS;
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
@@ -39,6 +39,7 @@
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/Constant.h"
+#include "llvm/IR/ConstantFPRange.h"
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DerivedTypes.h"
@@ -9474,6 +9475,69 @@ isImpliedCondICmps(CmpPredicate LPred, const Value *L0, const Value *L1,
   return std::nullopt;
 }
 
+/// Return true if LHS implies RHS (expanded to its components as "R0 RPred R1")
+/// is true.  Return false if LHS implies RHS is false. Otherwise, return
+/// std::nullopt if we can't infer anything.
+static std::optional<bool>
+isImpliedCondFCmps(FCmpInst::Predicate LPred, const Value *L0, const Value *L1,
+                   FCmpInst::Predicate RPred, const Value *R0, const Value *R1,
+                   const DataLayout &DL, bool LHSIsTrue) {
+  // The rest of the logic assumes the LHS condition is true.  If that's not the
+  // case, invert the predicate to make it so.
+  if (!LHSIsTrue)
+    LPred = FCmpInst::getInversePredicate(LPred);
+
+  // We can have non-canonical operands, so try to normalize any common operand
+  // to L0/R0.
+  if (L0 == R1) {
+    std::swap(R0, R1);
+    RPred = FCmpInst::getSwappedPredicate(RPred);
+  }
+  if (R0 == L1) {
+    std::swap(L0, L1);
+    LPred = FCmpInst::getSwappedPredicate(LPred);
+  }
+  if (L1 == R1) {
+    // If we have L0 == R0 and L1 == R1, then make L1/R1 the constants.
+    if (L0 != R0 || match(L0, m_ImmConstant())) {
+      std::swap(L0, L1);
+      LPred = ICmpInst::getSwappedCmpPredicate(LPred);
+      std::swap(R0, R1);
+      RPred = ICmpInst::getSwappedCmpPredicate(RPred);
+    }
+  }
+
+  // Can we infer anything when the two compares have matching operands?
+  if (L0 == R0 && L1 == R1) {
+    if ((LPred & RPred) == LPred)
+      return true;
+    if ((LPred & ~RPred) == LPred)
+      return false;
+  }
+
+  // See if we can infer anything if operand-0 matches and we have at least one
+  // constant.
+  const APFloat *L1C, *R1C;
+  if (L0 == R0 && match(L1, m_APFloat(L1C)) && match(R1, m_APFloat(R1C))) {
+    if (std::optional<ConstantFPRange> DomCR =
+            ConstantFPRange::makeExactFCmpRegion(LPred, *L1C)) {
+      if (std::optional<ConstantFPRange> ImpliedCR =
+              ConstantFPRange::makeExactFCmpRegion(RPred, *R1C)) {
+        if (ImpliedCR->contains(*DomCR))
+          return true;
+      }
+      if (std::optional<ConstantFPRange> ImpliedCR =
+              ConstantFPRange::makeExactFCmpRegion(
+                  FCmpInst::getInversePredicate(RPred), *R1C)) {
+        if (ImpliedCR->contains(*DomCR))
+          return false;
+      }
+    }
+  }
+
+  return std::nullopt;
+}
+
 /// Return true if LHS implies RHS is true.  Return false if LHS implies RHS is
 /// false.  Otherwise, return std::nullopt if we can't infer anything.  We
 /// expect the RHS to be an icmp and the LHS to be an 'and', 'or', or a 'select'
@@ -9529,15 +9593,24 @@ llvm::isImpliedCondition(const Value *LHS, CmpPredicate RHSPred,
     LHSIsTrue = !LHSIsTrue;
 
   // Both LHS and RHS are icmps.
-  if (const auto *LHSCmp = dyn_cast<ICmpInst>(LHS))
-    return isImpliedCondICmps(LHSCmp->getCmpPredicate(), LHSCmp->getOperand(0),
-                              LHSCmp->getOperand(1), RHSPred, RHSOp0, RHSOp1,
-                              DL, LHSIsTrue);
-  const Value *V;
-  if (match(LHS, m_NUWTrunc(m_Value(V))))
-    return isImpliedCondICmps(CmpInst::ICMP_NE, V,
-                              ConstantInt::get(V->getType(), 0), RHSPred,
-                              RHSOp0, RHSOp1, DL, LHSIsTrue);
+  if (RHSOp0->getType()->getScalarType()->isIntOrPtrTy()) {
+    if (const auto *LHSCmp = dyn_cast<ICmpInst>(LHS))
+      return isImpliedCondICmps(LHSCmp->getCmpPredicate(),
+                                LHSCmp->getOperand(0), LHSCmp->getOperand(1),
+                                RHSPred, RHSOp0, RHSOp1, DL, LHSIsTrue);
+    const Value *V;
+    if (match(LHS, m_NUWTrunc(m_Value(V))))
+      return isImpliedCondICmps(CmpInst::ICMP_NE, V,
+                                ConstantInt::get(V->getType(), 0), RHSPred,
+                                RHSOp0, RHSOp1, DL, LHSIsTrue);
+  } else {
+    assert(RHSOp0->getType()->isFPOrFPVectorTy() &&
+           "Expected floating point type only!");
+    if (const auto *LHSCmp = dyn_cast<FCmpInst>(LHS))
+      return isImpliedCondFCmps(LHSCmp->getPredicate(), LHSCmp->getOperand(0),
+                                LHSCmp->getOperand(1), RHSPred, RHSOp0, RHSOp1,
+                                DL, LHSIsTrue);
+  }
 
   /// The LHS should be an 'or', 'and', or a 'select' instruction.  We expect
   /// the RHS to be an icmp.
@@ -9574,6 +9647,13 @@ std::optional<bool> llvm::isImpliedCondition(const Value *LHS, const Value *RHS,
       return InvertRHS ? !*Implied : *Implied;
     return std::nullopt;
   }
+  if (const FCmpInst *RHSCmp = dyn_cast<FCmpInst>(RHS)) {
+    if (auto Implied = isImpliedCondition(
+            LHS, RHSCmp->getPredicate(), RHSCmp->getOperand(0),
+            RHSCmp->getOperand(1), DL, LHSIsTrue, Depth))
+      return InvertRHS ? !*Implied : *Implied;
+    return std::nullopt;
+  }
 
   const Value *V;
   if (match(RHS, m_NUWTrunc(m_Value(V)))) {
diff --git a/llvm/test/CodeGen/AMDGPU/sgpr-copy.ll b/llvm/test/CodeGen/AMDGPU/sgpr-copy.ll
@@ -256,7 +256,7 @@ endif:                                            ; preds = %else, %if
 define amdgpu_kernel void @copy1(ptr addrspace(1) %out, ptr addrspace(1) %in0) {
 entry:
   %tmp = load float, ptr addrspace(1) %in0
-  %tmp1 = fcmp oeq float %tmp, 0.000000e+00
+  %tmp1 = fcmp one float %tmp, 0.000000e+00
   br i1 %tmp1, label %if0, label %endif
 
 if0:                                              ; preds = %entry
diff --git a/llvm/test/Transforms/InstCombine/clamp-to-minmax.ll b/llvm/test/Transforms/InstCombine/clamp-to-minmax.ll
@@ -172,10 +172,8 @@ define float @clamp_negative_wrong_const(float %x) {
 ; Like @clamp_test_1 but both are min
 define float @clamp_negative_same_op(float %x) {
 ; CHECK-LABEL: @clamp_negative_same_op(
-; CHECK-NEXT:    [[INNER_CMP_INV:%.*]] = fcmp fast oge float [[X:%.*]], 2.550000e+02
-; CHECK-NEXT:    [[INNER_SEL:%.*]] = select nnan ninf i1 [[INNER_CMP_INV]], float 2.550000e+02, float [[X]]
-; CHECK-NEXT:    [[OUTER_CMP:%.*]] = fcmp fast ult float [[X]], 1.000000e+00
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[OUTER_CMP]], float [[INNER_SEL]], float 1.000000e+00
+; CHECK-NEXT:    [[OUTER_CMP_INV:%.*]] = fcmp fast oge float [[X:%.*]], 1.000000e+00
+; CHECK-NEXT:    [[R:%.*]] = select nnan ninf i1 [[OUTER_CMP_INV]], float 1.000000e+00, float [[X]]
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %inner_cmp = fcmp fast ult float %x, 255.0
diff --git a/llvm/test/Transforms/InstSimplify/domcondition.ll b/llvm/test/Transforms/InstSimplify/domcondition.ll
@@ -278,3 +278,210 @@ end:
 }
 
 declare void @foo(i32)
+
+
+define i1 @simplify_fcmp_implied_by_dom_cond_range_true(float %x) {
+; CHECK-LABEL: @simplify_fcmp_implied_by_dom_cond_range_true(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    ret i1 true
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp = fcmp olt float %x, 0.0
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %cmp2 = fcmp olt float %x, 1.0
+  ret i1 %cmp2
+
+if.else:
+  ret i1 false
+}
+
+define i1 @simplify_fcmp_in_else_implied_by_dom_cond_range_true(float %x) {
+; CHECK-LABEL: @simplify_fcmp_in_else_implied_by_dom_cond_range_true(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[X:%.*]], 1.000000e+00
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    ret i1 true
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 true
+;
+  %cmp = fcmp olt float %x, 1.0
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  ret i1 true
+
+if.else:
+  %cmp2 = fcmp uge float %x, 0.5
+  ret i1 %cmp2
+}
+
+define i1 @simplify_fcmp_implied_by_dom_cond_range_false(float %x) {
+; CHECK-LABEL: @simplify_fcmp_implied_by_dom_cond_range_false(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    ret i1 false
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp = fcmp olt float %x, 0.0
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %cmp2 = fcmp ogt float %x, 1.0
+  ret i1 %cmp2
+
+if.else:
+  ret i1 false
+}
+
+define i1 @simplify_fcmp_implied_by_dom_cond_pred_true(float %x, float %y) {
+; CHECK-LABEL: @simplify_fcmp_implied_by_dom_cond_pred_true(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    ret i1 true
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp = fcmp olt float %x, %y
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %cmp2 = fcmp ole float %x, %y
+  ret i1 %cmp2
+
+if.else:
+  ret i1 false
+}
+
+define i1 @simplify_fcmp_implied_by_dom_cond_pred_false(float %x, float %y) {
+; CHECK-LABEL: @simplify_fcmp_implied_by_dom_cond_pred_false(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    ret i1 false
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp = fcmp olt float %x, %y
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %cmp2 = fcmp ogt float %x, %y
+  ret i1 %cmp2
+
+if.else:
+  ret i1 false
+}
+
+define i1 @simplify_fcmp_implied_by_dom_cond_pred_commuted(float %x, float %y) {
+; CHECK-LABEL: @simplify_fcmp_implied_by_dom_cond_pred_commuted(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    ret i1 true
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp = fcmp olt float %x, %y
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %cmp2 = fcmp oge float %y, %x
+  ret i1 %cmp2
+
+if.else:
+  ret i1 false
+}
+
+; Negative tests
+
+define i1 @simplify_fcmp_implied_by_dom_cond_wrong_range(float %x) {
+; CHECK-LABEL: @simplify_fcmp_implied_by_dom_cond_wrong_range(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[CMP2:%.*]] = fcmp olt float [[X]], -1.000000e+00
+; CHECK-NEXT:    ret i1 [[CMP2]]
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp = fcmp olt float %x, 0.0
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %cmp2 = fcmp olt float %x, -1.0
+  ret i1 %cmp2
+
+if.else:
+  ret i1 false
+}
+
+define i1 @simplify_fcmp_implied_by_dom_cond_range_mismatched_operand(float %x, float %y) {
+; CHECK-LABEL: @simplify_fcmp_implied_by_dom_cond_range_mismatched_operand(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[CMP2:%.*]] = fcmp olt float [[Y:%.*]], 1.000000e+00
+; CHECK-NEXT:    ret i1 [[CMP2]]
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp = fcmp olt float %x, 0.0
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %cmp2 = fcmp olt float %y, 1.0
+  ret i1 %cmp2
+
+if.else:
+  ret i1 false
+}
+
+define i1 @simplify_fcmp_implied_by_dom_cond_wrong_pred(float %x, float %y) {
+; CHECK-LABEL: @simplify_fcmp_implied_by_dom_cond_wrong_pred(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp ole float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[CMP2:%.*]] = fcmp olt float [[X]], [[Y]]
+; CHECK-NEXT:    ret i1 [[CMP2]]
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp = fcmp ole float %x, %y
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %cmp2 = fcmp olt float %x, %y
+  ret i1 %cmp2
+
+if.else:
+  ret i1 false
+}
+
+define i1 @simplify_fcmp_implied_by_dom_cond_pred_mismatched_operand(float %x, float %y, float %z) {
+; CHECK-LABEL: @simplify_fcmp_implied_by_dom_cond_pred_mismatched_operand(
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[CMP2:%.*]] = fcmp ole float [[X]], [[Z:%.*]]
+; CHECK-NEXT:    ret i1 [[CMP2]]
+; CHECK:       if.else:
+; CHECK-NEXT:    ret i1 false
+;
+  %cmp = fcmp olt float %x, %y
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %cmp2 = fcmp ole float %x, %z
+  ret i1 %cmp2
+
+if.else:
+  ret i1 false
+}
