[llvm] 5d39cae - [InstCombine] Generalise optimisation of redundant floating point comparisons with `ConstantFPRange` (#159315)

[via llvm-commits]

Author: Rajveer Singh Bharadwaj
Date: 2025-09-20T12:42:17Z
New Revision: 5d39cae6ba30d84e48b5374239dbd4e20d1d4870

URL: https://github.com/llvm/llvm-project/commit/5d39cae6ba30d84e48b5374239dbd4e20d1d4870
DIFF: https://github.com/llvm/llvm-project/commit/5d39cae6ba30d84e48b5374239dbd4e20d1d4870.diff

LOG: [InstCombine] Generalise optimisation of redundant floating point comparisons with `ConstantFPRange` (#159315)

Follow up of #158097

Similar to `simplifyAndOrOfICmpsWithConstants`, we can do so for
floating point comparisons.

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp
    llvm/test/Transforms/InstCombine/redundant-fcmp.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 17933ed03d587..a90b618607ad6 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -35,6 +35,7 @@
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Analysis/VectorUtils.h"
+#include "llvm/IR/ConstantFPRange.h"
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Dominators.h"
@@ -1812,6 +1813,46 @@ static Value *simplifyOrOfICmps(ICmpInst *Op0, ICmpInst *Op1,
   return nullptr;
 }
 
+/// Test if a pair of compares with a shared operand and 2 constants has an
+/// empty set intersection, full set union, or if one compare is a superset of
+/// the other.
+static Value *simplifyAndOrOfFCmpsWithConstants(FCmpInst *Cmp0, FCmpInst *Cmp1,
+                                                bool IsAnd) {
+  // Look for this pattern: {and/or} (fcmp X, C0), (fcmp X, C1)).
+  if (Cmp0->getOperand(0) != Cmp1->getOperand(0))
+    return nullptr;
+
+  const APFloat *C0, *C1;
+  if (!match(Cmp0->getOperand(1), m_APFloat(C0)) ||
+      !match(Cmp1->getOperand(1), m_APFloat(C1)))
+    return nullptr;
+
+  auto Range0 = ConstantFPRange::makeExactFCmpRegion(
+      IsAnd ? Cmp0->getPredicate() : Cmp0->getInversePredicate(), *C0);
+  auto Range1 = ConstantFPRange::makeExactFCmpRegion(
+      IsAnd ? Cmp1->getPredicate() : Cmp1->getInversePredicate(), *C1);
+
+  if (!Range0 || !Range1)
+    return nullptr;
+
+  // For and-of-compares, check if the intersection is empty:
+  // (fcmp X, C0) && (fcmp X, C1) --> empty set --> false
+  if (Range0->intersectWith(*Range1).isEmptySet())
+    return ConstantInt::getBool(Cmp0->getType(), !IsAnd);
+
+  // Is one range a superset of the other?
+  // If this is and-of-compares, take the smaller set:
+  // (fcmp ogt X, 4) && (fcmp ogt X, 42) --> fcmp ogt X, 42
+  // If this is or-of-compares, take the larger set:
+  // (fcmp ogt X, 4) || (fcmp ogt X, 42) --> fcmp ogt X, 4
+  if (Range0->contains(*Range1))
+    return Cmp1;
+  if (Range1->contains(*Range0))
+    return Cmp0;
+
+  return nullptr;
+}
+
 static Value *simplifyAndOrOfFCmps(const SimplifyQuery &Q, FCmpInst *LHS,
                                    FCmpInst *RHS, bool IsAnd) {
   Value *LHS0 = LHS->getOperand(0), *LHS1 = LHS->getOperand(1);
@@ -1850,34 +1891,8 @@ static Value *simplifyAndOrOfFCmps(const SimplifyQuery &Q, FCmpInst *LHS,
                  : ConstantInt::getBool(LHS->getType(), !IsAnd);
   }
 
-  Value *V0;
-  const APFloat *V0Op1, *V1Op1;
-  // (fcmp olt V0, V0Op1) || (fcmp olt V0, V1Op1)
-  //                      --> fcmp olt V0, max(V0Op1, V1Op1)
-  // (fcmp ogt V0, V0Op1) || (fcmp ogt V0, V1Op1)
-  //                      --> fcmp ogt V0, max(V0Op1, V1Op1)
-  //
-  // (fcmp olt V0, V0Op1) && (fcmp olt V0, V1Op1)
-  //                      --> fcmp olt V0, min(V0Op1, V1Op1)
-  // (fcmp ogt V0, V0Op1) && (fcmp ogt V0, V1Op1)
-  //                      --> fcmp ogt V0, min(V0Op1, V1Op1)
-  if (match(LHS, m_SpecificFCmp(FCmpInst::FCMP_OLT, m_Value(V0),
-                                m_APFloat(V0Op1))) &&
-      match(RHS, m_SpecificFCmp(FCmpInst::FCMP_OLT, m_Specific(V0),
-                                m_APFloat(V1Op1)))) {
-    if (*V0Op1 > *V1Op1)
-      return IsAnd ? RHS : LHS;
-    if (*V1Op1 > *V0Op1)
-      return IsAnd ? LHS : RHS;
-  } else if (match(LHS, m_SpecificFCmp(FCmpInst::FCMP_OGT, m_Value(V0),
-                                       m_APFloat(V0Op1))) &&
-             match(RHS, m_SpecificFCmp(FCmpInst::FCMP_OGT, m_Specific(V0),
-                                       m_APFloat(V1Op1)))) {
-    if (*V0Op1 < *V1Op1)
-      return IsAnd ? RHS : LHS;
-    if (*V1Op1 < *V0Op1)
-      return IsAnd ? LHS : RHS;
-  }
+  if (auto *V = simplifyAndOrOfFCmpsWithConstants(LHS, RHS, IsAnd))
+    return V;
 
   return nullptr;
 }

diff  --git a/llvm/test/Transforms/InstCombine/redundant-fcmp.ll b/llvm/test/Transforms/InstCombine/redundant-fcmp.ll
index 0f5fe9fb9a1b2..7f579ed9f25c5 100644
--- a/llvm/test/Transforms/InstCombine/redundant-fcmp.ll
+++ b/llvm/test/Transforms/InstCombine/redundant-fcmp.ll
@@ -117,10 +117,7 @@ define i1 @or_fcmp_redundant_and4(double %v0) {
 
 define i1 @or_fcmp_redundant_and_neg1(double %v0) {
 ; CHECK-LABEL: @or_fcmp_redundant_and_neg1(
-; CHECK-NEXT:    [[V1:%.*]] = fcmp olt double [[V0:%.*]], 1.000000e-02
-; CHECK-NEXT:    [[V2:%.*]] = fcmp ogt double [[V0]], 1.990000e+00
-; CHECK-NEXT:    [[V3:%.*]] = and i1 [[V1]], [[V2]]
-; CHECK-NEXT:    ret i1 [[V3]]
+; CHECK-NEXT:    ret i1 false
 ;
   %v1 = fcmp olt double %v0, 1.000000e-02
   %v2 = fcmp ogt double %v0, 1.990000e+00