[InstCombine] Remove m_OneUse requirement for max, but not min (#81505)

If it is ever determined that min doesn't need one-use, then we can
remove the one-use requirement entirely.

Author: AZero13

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -2288,11 +2288,18 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
 
     // max X, -X --> fabs X
     // min X, -X --> -(fabs X)
-    // TODO: Remove one-use limitation? That is obviously better for max.
-    //       It would be an extra instruction for min (fnabs), but that is
-    //       still likely better for analysis and codegen.
-    if ((match(Arg0, m_OneUse(m_FNeg(m_Value(X)))) && Arg1 == X) ||
-        (match(Arg1, m_OneUse(m_FNeg(m_Value(X)))) && Arg0 == X)) {
+    // TODO: Remove one-use limitation? That is obviously better for max,
+    // hence why we don't check for one-use for that. However,
+    // it would be an extra instruction for min (fnabs), but
+    // that is still likely better for analysis and codegen.
+    auto IsMinMaxOrXNegX = [IID, &X](Value *Op0, Value *Op1) {
+      if (match(Op0, m_FNeg(m_Value(X))) && match(Op1, m_Specific(X)))
+        return Op0->hasOneUse() ||
+               (IID != Intrinsic::minimum && IID != Intrinsic::minnum);
+      return false;
+    };
+
+    if (IsMinMaxOrXNegX(Arg0, Arg1) || IsMinMaxOrXNegX(Arg1, Arg0)) {
       Value *R = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, II);
       if (IID == Intrinsic::minimum || IID == Intrinsic::minnum)
         R = Builder.CreateFNegFMF(R, II);

llvm/test/Transforms/InstCombine/maximum.ll

@@ -436,11 +436,24 @@ define float @negated_op_extra_use(float %x) {
 ; CHECK-LABEL: @negated_op_extra_use(
 ; CHECK-NEXT:    [[NEGX:%.*]] = fneg float [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[NEGX]])
-; CHECK-NEXT:    [[R:%.*]] = call float @llvm.maximum.f32(float [[NEGX]], float [[X]])
+; CHECK-NEXT:    [[R:%.*]] = call float @llvm.fabs.f32(float [[X]])
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %negx = fneg float %x
   call void @use(float %negx)
   %r = call float @llvm.maximum.f32(float %negx, float %x)
   ret float %r
 }
+
+define float @negated_op_extra_use_comm(float %x) {
+; CHECK-LABEL: @negated_op_extra_use_comm(
+; CHECK-NEXT:    [[NEGX:%.*]] = fneg float [[X:%.*]]
+; CHECK-NEXT:    call void @use(float [[NEGX]])
+; CHECK-NEXT:    [[R:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[R]]
+;
+  %negx = fneg float %x
+  call void @use(float %negx)
+  %r = call float @llvm.maximum.f32(float %x, float %negx)
+  ret float %r
+}

llvm/test/Transforms/InstCombine/maxnum.ll

@@ -458,11 +458,24 @@ define float @negated_op_extra_use(float %x) {
 ; CHECK-LABEL: @negated_op_extra_use(
 ; CHECK-NEXT:    [[NEGX:%.*]] = fneg float [[X:%.*]]
 ; CHECK-NEXT:    call void @use(float [[NEGX]])
-; CHECK-NEXT:    [[R:%.*]] = call float @llvm.maxnum.f32(float [[NEGX]], float [[X]])
+; CHECK-NEXT:    [[R:%.*]] = call float @llvm.fabs.f32(float [[X]])
 ; CHECK-NEXT:    ret float [[R]]
 ;
   %negx = fneg float %x
   call void @use(float %negx)
   %r = call float @llvm.maxnum.f32(float %negx, float %x)
   ret float %r
 }
+
+define float @negated_op_extra_use_comm(float %x) {
+; CHECK-LABEL: @negated_op_extra_use_comm(
+; CHECK-NEXT:    [[NEGX:%.*]] = fneg float [[X:%.*]]
+; CHECK-NEXT:    call void @use(float [[NEGX]])
+; CHECK-NEXT:    [[R:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[R]]
+;
+  %negx = fneg float %x
+  call void @use(float %negx)
+  %r = call float @llvm.maxnum.f32(float %x, float %negx)
+  ret float %r
+}