[llvm] [InstCombine] FP fold, cond ? x : -x == 0 into x == 0 #85250 (PR #85673)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (SahilPatidar)

<details>
<summary>Changes</summary>

Resolve #<!-- -->85250 
Alive2: https://alive2.llvm.org/ce/z/7DMRCy

---
Full diff: https://github.com/llvm/llvm-project/pull/85673.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp (+7) 
- (modified) llvm/test/Transforms/InstCombine/fcmp.ll (+107) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 0dce0077bf1588..6d5ef3c6718554 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -7972,6 +7972,13 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
   Constant *RHSC;
   if (match(Op0, m_Instruction(LHSI)) && match(Op1, m_Constant(RHSC))) {
     switch (LHSI->getOpcode()) {
+    case Instruction::Select:
+      if ((Pred == FCmpInst::FCMP_UEQ || Pred == FCmpInst::FCMP_OEQ ||
+           Pred == FCmpInst::FCMP_UNE || Pred == FCmpInst::FCMP_ONE) &&
+          match(LHSI, m_Select(m_Value(), m_Value(X), m_FNeg(m_Value(Y)))) &&
+          X == Y && match(RHSC, m_AnyZeroFP()))
+        return new FCmpInst(Pred, X, RHSC);
+      break;
     case Instruction::PHI:
       if (Instruction *NV = foldOpIntoPhi(I, cast<PHINode>(LHSI)))
         return NV;
diff --git a/llvm/test/Transforms/InstCombine/fcmp.ll b/llvm/test/Transforms/InstCombine/fcmp.ll
index 159c84d0dd8aa9..ac5476159dd4ef 100644
--- a/llvm/test/Transforms/InstCombine/fcmp.ll
+++ b/llvm/test/Transforms/InstCombine/fcmp.ll
@@ -1284,3 +1284,110 @@ define <1 x i1> @bitcast_1vec_eq0(i32 %x) {
   %cmp = fcmp oeq <1 x float> %f, zeroinitializer
   ret <1 x i1> %cmp
 }
+
+define i1 @fcmp_ueq_sel_x_negx(float %x) {
+; CHECK-LABEL: @fcmp_ueq_sel_x_negx(
+; CHECK-NEXT:    [[RES:%.*]] = fcmp ueq float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %f = fcmp ueq float %x, 0.000000e+00
+  %neg = fneg fast float %x
+  %sel = select i1 %f, float %x, float %neg
+  %res = fcmp ueq float %sel, 0.000000e+00
+  ret i1 %res
+}
+
+define i1 @fcmp_une_sel_x_negx(float %x) {
+; CHECK-LABEL: @fcmp_une_sel_x_negx(
+; CHECK-NEXT:    [[RES:%.*]] = fcmp une float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %f = fcmp une float %x, 0.000000e+00
+  %neg = fneg fast float %x
+  %sel = select i1 %f, float %x, float %neg
+  %res = fcmp une float %sel, 0.000000e+00
+  ret i1 %res
+}
+
+define i1 @fcmp_oeq_sel_x_negx(float %x) {
+; CHECK-LABEL: @fcmp_oeq_sel_x_negx(
+; CHECK-NEXT:    [[RES:%.*]] = fcmp oeq float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %f = fcmp oeq float %x, 0.000000e+00
+  %neg = fneg fast float %x
+  %sel = select i1 %f, float %x, float %neg
+  %res = fcmp oeq float %sel, 0.000000e+00
+  ret i1 %res
+}
+
+define i1 @fcmp_one_sel_x_negx(float %x) {
+; CHECK-LABEL: @fcmp_one_sel_x_negx(
+; CHECK-NEXT:    [[RES:%.*]] = fcmp one float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %f = fcmp one float %x, 0.000000e+00
+  %neg = fneg fast float %x
+  %sel = select i1 %f, float %x, float %neg
+  %res = fcmp one float %sel, 0.000000e+00
+  ret i1 %res
+}
+
+define <8 x i1> @fcmp_ueq_sel_x_negx_vec(<8 x float> %x) {
+; CHECK-LABEL: @fcmp_ueq_sel_x_negx_vec(
+; CHECK-NEXT:    [[RES:%.*]] = fcmp ueq <8 x float> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    ret <8 x i1> [[RES]]
+;
+  %f = fcmp ueq <8 x float> %x, zeroinitializer
+  %neg = fneg fast <8 x float> %x
+  %sel = select <8 x i1> %f, <8 x float> %x, <8 x float> %neg
+  %res = fcmp ueq <8 x float> %sel, zeroinitializer
+  ret <8 x i1> %res
+}
+
+define <8 x i1> @fcmp_une_sel_x_negx_vec(<8 x float> %x) {
+; CHECK-LABEL: @fcmp_une_sel_x_negx_vec(
+; CHECK-NEXT:    [[RES:%.*]] = fcmp une <8 x float> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    ret <8 x i1> [[RES]]
+;
+  %f = fcmp une <8 x float> %x, zeroinitializer
+  %neg = fneg fast <8 x float> %x
+  %sel = select <8 x i1> %f, <8 x float> %x, <8 x float> %neg
+  %res = fcmp une <8 x float> %sel, zeroinitializer
+  ret <8 x i1> %res
+}
+
+define <8 x i1> @fcmp_oeq_sel_x_negx_vec(<8 x float> %x) {
+; CHECK-LABEL: @fcmp_oeq_sel_x_negx_vec(
+; CHECK-NEXT:    [[RES:%.*]] = fcmp oeq <8 x float> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    ret <8 x i1> [[RES]]
+;
+  %f = fcmp oeq <8 x float> %x, zeroinitializer
+  %neg = fneg fast <8 x float> %x
+  %sel = select <8 x i1> %f, <8 x float> %x, <8 x float> %neg
+  %res = fcmp oeq <8 x float> %sel, zeroinitializer
+  ret <8 x i1> %res
+}
+
+define <8 x i1> @fcmp_one_sel_x_negx_vec(<8 x float> %x) {
+; CHECK-LABEL: @fcmp_one_sel_x_negx_vec(
+; CHECK-NEXT:    [[RES:%.*]] = fcmp one <8 x float> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    ret <8 x i1> [[RES]]
+;
+  %f = fcmp one <8 x float> %x, zeroinitializer
+  %neg = fneg fast <8 x float> %x
+  %sel = select <8 x i1> %f, <8 x float> %x, <8 x float> %neg
+  %res = fcmp one <8 x float> %sel, zeroinitializer
+  ret <8 x i1> %res
+}
+
+define i1 @fcmp_sel_x_negx_with_any_cond(float %x, i1 %c) {
+; CHECK-LABEL: @fcmp_sel_x_negx_with_any_cond(
+; CHECK-NEXT:    [[RES:%.*]] = fcmp ueq float [[X:%.*]], 0.000000e+00
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %neg = fneg float %x
+  %sel = select i1 %c, float %x, float %neg
+  %res = fcmp ueq float %sel, 0.000000e+00
+  ret i1 %res
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/85673