[llvm] [InstCombine] Extend `foldSelectInstWithICmpConst` to handle minmax (PR #125346)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

This patch extends https://github.com/llvm/llvm-project/commit/f6bb156fb10cd83953a34f75b78835cdf399ee8b to handle minmax intrinsics.
Motivating case: https://alive2.llvm.org/ce/z/JFKbYn 
Addresses a regression caused by https://github.com/llvm/llvm-project/pull/121958.


---
Full diff: https://github.com/llvm/llvm-project/pull/125346.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp (+24-12) 
- (modified) llvm/test/Transforms/InstCombine/select-min-max.ll (+63) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 29c5cef84ccdb7..382078e85a17b6 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1771,26 +1771,38 @@ static Value *foldSelectInstWithICmpConst(SelectInst &SI, ICmpInst *ICI,
       return Builder.CreateBinaryIntrinsic(Intrinsic::smin, V, TVal);
   }
 
-  BinaryOperator *BO;
+  // Fold icmp(X) ? f(X) : C to f(X) when f(X) is guaranteed to be equal to C
+  // for all X in the exact range of the inverse predicate.
+  Instruction *Op;
   const APInt *C;
   CmpInst::Predicate CPred;
-  if (match(&SI, m_Select(m_Specific(ICI), m_APInt(C), m_BinOp(BO))))
+  if (match(&SI, m_Select(m_Specific(ICI), m_APInt(C), m_Instruction(Op))))
     CPred = ICI->getPredicate();
-  else if (match(&SI, m_Select(m_Specific(ICI), m_BinOp(BO), m_APInt(C))))
+  else if (match(&SI, m_Select(m_Specific(ICI), m_Instruction(Op), m_APInt(C))))
     CPred = ICI->getInversePredicate();
   else
     return nullptr;
 
-  const APInt *BinOpC;
-  if (!match(BO, m_BinOp(m_Specific(V), m_APInt(BinOpC))))
-    return nullptr;
-
-  ConstantRange R = ConstantRange::makeExactICmpRegion(CPred, *CmpC)
-                        .binaryOp(BO->getOpcode(), *BinOpC);
-  if (R == *C) {
-    BO->dropPoisonGeneratingFlags();
-    return BO;
+  ConstantRange InvDomCR = ConstantRange::makeExactICmpRegion(CPred, *CmpC);
+  const APInt *OpC;
+  if (match(Op, m_BinOp(m_Specific(V), m_APInt(OpC)))) {
+    ConstantRange R = InvDomCR.binaryOp(
+        static_cast<Instruction::BinaryOps>(Op->getOpcode()), *OpC);
+    if (R == *C) {
+      Op->dropPoisonGeneratingFlags();
+      return Op;
+    }
+  }
+  if (auto *MMI = dyn_cast<MinMaxIntrinsic>(Op);
+      MMI && MMI->getLHS() == V && match(MMI->getRHS(), m_APInt(OpC))) {
+    ConstantRange R = ConstantRange::intrinsic(MMI->getIntrinsicID(),
+                                               {InvDomCR, ConstantRange(*OpC)});
+    if (R == *C) {
+      MMI->dropPoisonGeneratingAnnotations();
+      return MMI;
+    }
   }
+
   return nullptr;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/select-min-max.ll b/llvm/test/Transforms/InstCombine/select-min-max.ll
index f13223284e6a68..0430fcd5ad3700 100644
--- a/llvm/test/Transforms/InstCombine/select-min-max.ll
+++ b/llvm/test/Transforms/InstCombine/select-min-max.ll
@@ -301,3 +301,66 @@ define i8 @not_smin_swap(i8 %i41, i8 %i43) {
   %spec.select = select i1 %i44, i8 %i46, i8 0
   ret i8 %spec.select
 }
+
+define i8 @sel_umin_constant(i8 %x) {
+; CHECK-LABEL: @sel_umin_constant(
+; CHECK-NEXT:    [[UMIN:%.*]] = call i8 @llvm.umin.i8(i8 [[X:%.*]], i8 16)
+; CHECK-NEXT:    ret i8 [[UMIN]]
+;
+  %cmp = icmp sgt i8 %x, -1
+  %umin = call i8 @llvm.umin.i8(i8 %x, i8 16)
+  %sel = select i1 %cmp, i8 %umin, i8 16
+  ret i8 %sel
+}
+
+define i8 @sel_constant_smax_with_range_attr(i8 %x) {
+; CHECK-LABEL: @sel_constant_smax_with_range_attr(
+; CHECK-NEXT:    [[SEL:%.*]] = call i8 @llvm.smax.i8(i8 [[X:%.*]], i8 16)
+; CHECK-NEXT:    ret i8 [[SEL]]
+;
+  %cmp = icmp slt i8 %x, 0
+  %smax = call range(i8 8, 16) i8 @llvm.smax.i8(i8 %x, i8 16)
+  %sel = select i1 %cmp, i8 16, i8 %smax
+  ret i8 %sel
+}
+
+; Negative tests
+
+define i8 @sel_umin_constant_mismatch(i8 %x) {
+; CHECK-LABEL: @sel_umin_constant_mismatch(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[X:%.*]], -1
+; CHECK-NEXT:    [[UMIN:%.*]] = call i8 @llvm.umin.i8(i8 [[X]], i8 16)
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[UMIN]], i8 15
+; CHECK-NEXT:    ret i8 [[SEL]]
+;
+  %cmp = icmp sgt i8 %x, -1
+  %umin = call i8 @llvm.umin.i8(i8 %x, i8 16)
+  %sel = select i1 %cmp, i8 %umin, i8 15
+  ret i8 %sel
+}
+
+define i8 @sel_umin_constant_op_mismatch(i8 %x, i8 %y) {
+; CHECK-LABEL: @sel_umin_constant_op_mismatch(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[X:%.*]], -1
+; CHECK-NEXT:    [[UMIN:%.*]] = call i8 @llvm.umin.i8(i8 [[Y:%.*]], i8 16)
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8 [[UMIN]], i8 16
+; CHECK-NEXT:    ret i8 [[SEL]]
+;
+  %cmp = icmp sgt i8 %x, -1
+  %umin = call i8 @llvm.umin.i8(i8 %y, i8 16)
+  %sel = select i1 %cmp, i8 %umin, i8 16
+  ret i8 %sel
+}
+
+define i8 @sel_umin_non_constant(i8 %x, i8 %y) {
+; CHECK-LABEL: @sel_umin_non_constant(
+; CHECK-NEXT:    [[UMIN:%.*]] = call i8 @llvm.umin.i8(i8 [[X:%.*]], i8 16)
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i8 [[X]], 0
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP1]], i8 [[Y:%.*]], i8 [[UMIN]]
+; CHECK-NEXT:    ret i8 [[SEL]]
+;
+  %cmp = icmp sgt i8 %x, -1
+  %umin = call i8 @llvm.umin.i8(i8 %x, i8 16)
+  %sel = select i1 %cmp, i8 %umin, i8 %y
+  ret i8 %sel
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/125346