[InstCombine] Fix frexp(frexp(x)) -> frexp(x) fold (#138837)

Fixes #138819

When frexp is applied twice, the second result should be zero.

Author: el-ev

llvm/lib/Analysis/InstructionSimplify.cpp

@@ -6377,15 +6377,6 @@ static Value *simplifyUnaryIntrinsic(Function *F, Value *Op0,
     if (isSplatValue(Op0))
       return Op0;
     break;
-  case Intrinsic::frexp: {
-    // Frexp is idempotent with the added complication of the struct return.
-    if (match(Op0, m_ExtractValue<0>(m_Value(X)))) {
-      if (match(X, m_Intrinsic<Intrinsic::frexp>(m_Value())))
-        return X;
-    }
-
-    break;
-  }
   default:
     break;
   }

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -3811,6 +3811,21 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     }
     break;
   }
+  case Intrinsic::frexp: {
+    Value *X;
+    // The first result is idempotent with the added complication of the struct
+    // return, and the second result is zero because the value is already
+    // normalized.
+    if (match(II->getArgOperand(0), m_ExtractValue<0>(m_Value(X)))) {
+      if (match(X, m_Intrinsic<Intrinsic::frexp>(m_Value()))) {
+        X = Builder.CreateInsertValue(
+            X, Constant::getNullValue(II->getType()->getStructElementType(1)),
+            1);
+        return replaceInstUsesWith(*II, X);
+      }
+    }
+    break;
+  }
   default: {
     // Handle target specific intrinsics
     std::optional<Instruction *> V = targetInstCombineIntrinsic(*II);

llvm/test/CodeGen/AMDGPU/frexp-constant-fold.ll

@@ -10,9 +10,9 @@ define { float, i32 } @frexp_frexp(float %x) {
 ; CHECK-LABEL: frexp_frexp:
 ; CHECK:       ; %bb.0:
 ; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; CHECK-NEXT:    v_frexp_mant_f32_e32 v2, v0
-; CHECK-NEXT:    v_frexp_exp_i32_f32_e32 v1, v0
-; CHECK-NEXT:    v_mov_b32_e32 v0, v2
+; CHECK-NEXT:    v_frexp_mant_f32_e32 v1, v0
+; CHECK-NEXT:    v_frexp_mant_f32_e32 v0, v1
+; CHECK-NEXT:    v_frexp_exp_i32_f32_e32 v1, v1
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
   %frexp0 = call { float, i32 } @llvm.frexp.f32.i32(float %x)
   %frexp0.0 = extractvalue { float, i32 } %frexp0, 0
@@ -24,12 +24,12 @@ define { <2 x float>, <2 x i32> } @frexp_frexp_vector(<2 x float> %x) {
 ; CHECK-LABEL: frexp_frexp_vector:
 ; CHECK:       ; %bb.0:
 ; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; CHECK-NEXT:    v_frexp_mant_f32_e32 v4, v0
-; CHECK-NEXT:    v_frexp_mant_f32_e32 v5, v1
-; CHECK-NEXT:    v_frexp_exp_i32_f32_e32 v2, v0
-; CHECK-NEXT:    v_frexp_exp_i32_f32_e32 v3, v1
-; CHECK-NEXT:    v_mov_b32_e32 v0, v4
-; CHECK-NEXT:    v_mov_b32_e32 v1, v5
+; CHECK-NEXT:    v_frexp_mant_f32_e32 v3, v1
+; CHECK-NEXT:    v_frexp_mant_f32_e32 v2, v0
+; CHECK-NEXT:    v_frexp_mant_f32_e32 v0, v2
+; CHECK-NEXT:    v_frexp_mant_f32_e32 v1, v3
+; CHECK-NEXT:    v_frexp_exp_i32_f32_e32 v2, v2
+; CHECK-NEXT:    v_frexp_exp_i32_f32_e32 v3, v3
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
   %frexp0 = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> %x)
   %frexp0.0 = extractvalue { <2 x float>, <2 x i32> } %frexp0, 0

llvm/test/Transforms/InstSimplify/frexp.ll renamed to llvm/test/Transforms/InstCombine/frexp.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
-; RUN: opt -S -passes=instsimplify %s | FileCheck %s
+; RUN: opt -S -passes=instcombine %s | FileCheck %s
 
 declare { float, i32 } @llvm.frexp.f32.i32(float)
 declare { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float>)
@@ -12,7 +12,8 @@ define { float, i32 } @frexp_frexp(float %x) {
 ; CHECK-LABEL: define { float, i32 } @frexp_frexp(
 ; CHECK-SAME: float [[X:%.*]]) {
 ; CHECK-NEXT:    [[FREXP0:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[X]])
-; CHECK-NEXT:    ret { float, i32 } [[FREXP0]]
+; CHECK-NEXT:    [[FREXP1:%.*]] = insertvalue { float, i32 } [[FREXP0]], i32 0, 1
+; CHECK-NEXT:    ret { float, i32 } [[FREXP1]]
 ;
   %frexp0 = call { float, i32 } @llvm.frexp.f32.i32(float %x)
   %frexp0.0 = extractvalue { float, i32 } %frexp0, 0
@@ -24,7 +25,8 @@ define { <2 x float>, <2 x i32> } @frexp_frexp_vector(<2 x float> %x) {
 ; CHECK-LABEL: define { <2 x float>, <2 x i32> } @frexp_frexp_vector(
 ; CHECK-SAME: <2 x float> [[X:%.*]]) {
 ; CHECK-NEXT:    [[FREXP0:%.*]] = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> [[X]])
-; CHECK-NEXT:    ret { <2 x float>, <2 x i32> } [[FREXP0]]
+; CHECK-NEXT:    [[FREXP1:%.*]] = insertvalue { <2 x float>, <2 x i32> } [[FREXP0]], <2 x i32> zeroinitializer, 1
+; CHECK-NEXT:    ret { <2 x float>, <2 x i32> } [[FREXP1]]
 ;
   %frexp0 = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> %x)
   %frexp0.0 = extractvalue { <2 x float>, <2 x i32> } %frexp0, 0
@@ -47,7 +49,8 @@ define { <vscale x 2 x float>, <vscale x 2 x i32> } @frexp_frexp_scalable_vector
 ; CHECK-LABEL: define { <vscale x 2 x float>, <vscale x 2 x i32> } @frexp_frexp_scalable_vector(
 ; CHECK-SAME: <vscale x 2 x float> [[X:%.*]]) {
 ; CHECK-NEXT:    [[FREXP0:%.*]] = call { <vscale x 2 x float>, <vscale x 2 x i32> } @llvm.frexp.nxv2f32.nxv2i32(<vscale x 2 x float> [[X]])
-; CHECK-NEXT:    ret { <vscale x 2 x float>, <vscale x 2 x i32> } [[FREXP0]]
+; CHECK-NEXT:    [[FREXP1:%.*]] = insertvalue { <vscale x 2 x float>, <vscale x 2 x i32> } [[FREXP0]], <vscale x 2 x i32> zeroinitializer, 1
+; CHECK-NEXT:    ret { <vscale x 2 x float>, <vscale x 2 x i32> } [[FREXP1]]
 ;
   %frexp0 = call { <vscale x 2 x float>, <vscale x 2 x i32> } @llvm.frexp.nxv2f32.nxv2i32(<vscale x 2 x float> %x)
   %frexp0.0 = extractvalue { <vscale x 2 x float>, <vscale x 2 x i32> } %frexp0, 0