[llvm] [InstCombine] InstCombine should fold frexp of select to select of frexp (PR #121227)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,130 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=instcombine -S < %s | FileCheck %s
+
+declare { float, i32 } @llvm.frexp.f32.i32(float)
+declare void @use(float)
+
+; Basic test case - constant in true position
+define float @test_select_frexp_basic(float %x, i1 %cond) {
+; CHECK-LABEL: define float @test_select_frexp_basic(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT:    [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[X]])
+; CHECK-NEXT:    [[FREXP_0:%.*]] = extractvalue { float, i32 } [[FREXP]], 0
+; CHECK-NEXT:    [[SELECT_FREXP:%.*]] = select i1 [[COND]], float 5.000000e-01, float [[FREXP_0]]
+; CHECK-NEXT:    ret float [[SELECT_FREXP]]
+;
+  %sel = select i1 %cond, float 1.000000e+00, float %x
+  %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+  %frexp.0 = extractvalue { float, i32 } %frexp, 0
+  ret float %frexp.0
+}
+
+; Test with constant in false position
+define float @test_select_frexp_const_false(float %x, i1 %cond) {
+; CHECK-LABEL: define float @test_select_frexp_const_false(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT:    [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[X]])
+; CHECK-NEXT:    [[FREXP_0:%.*]] = extractvalue { float, i32 } [[FREXP]], 0
+; CHECK-NEXT:    [[SELECT_FREXP:%.*]] = select i1 [[COND]], float [[FREXP_0]], float 5.000000e-01
+; CHECK-NEXT:    ret float [[SELECT_FREXP]]
+;
+  %sel = select i1 %cond, float %x, float 1.000000e+00
+  %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+  %frexp.0 = extractvalue { float, i32 } %frexp, 0
+  ret float %frexp.0
+}
+
+; Multi-use test
+define float @test_select_frexp_multi_use(float %x, i1 %cond) {
+; CHECK-LABEL: define float @test_select_frexp_multi_use(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND]], float 1.000000e+00, float [[X]]
+; CHECK-NEXT:    call void @use(float [[SEL]])
+; CHECK-NEXT:    [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[X]])
+; CHECK-NEXT:    [[FREXP_0:%.*]] = extractvalue { float, i32 } [[FREXP]], 0
+; CHECK-NEXT:    [[SELECT_FREXP:%.*]] = select i1 [[COND]], float 5.000000e-01, float [[FREXP_0]]
+; CHECK-NEXT:    ret float [[SELECT_FREXP]]
+;
+  %sel = select i1 %cond, float 1.000000e+00, float %x
+  call void @use(float %sel)
+  %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+  %frexp.0 = extractvalue { float, i32 } %frexp, 0
+  ret float %frexp.0
+}
+
+; Vector test - splat constant
+define <2 x float> @test_select_frexp_vec_splat(<2 x float> %x, <2 x i1> %cond) {
+; CHECK-LABEL: define <2 x float> @test_select_frexp_vec_splat(
+; CHECK-SAME: <2 x float> [[X:%.*]], <2 x i1> [[COND:%.*]]) {
+; CHECK-NEXT:    [[SEL:%.*]] = select <2 x i1> [[COND]], <2 x float> splat (float 1.000000e+00), <2 x float> [[X]]
+; CHECK-NEXT:    [[FREXP:%.*]] = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> [[SEL]])
+; CHECK-NEXT:    [[FREXP_0:%.*]] = extractvalue { <2 x float>, <2 x i32> } [[FREXP]], 0
+; CHECK-NEXT:    ret <2 x float> [[FREXP_0]]
+;
+  %sel = select <2 x i1> %cond, <2 x float> <float 1.000000e+00, float 1.000000e+00>, <2 x float> %x
+  %frexp = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> %sel)
+  %frexp.0 = extractvalue { <2 x float>, <2 x i32> } %frexp, 0
+  ret <2 x float> %frexp.0
+}
+
+; Vector test with poison
+define <2 x float> @test_select_frexp_vec_poison(<2 x float> %x, <2 x i1> %cond) {
+; CHECK-LABEL: define <2 x float> @test_select_frexp_vec_poison(
+; CHECK-SAME: <2 x float> [[X:%.*]], <2 x i1> [[COND:%.*]]) {
+; CHECK-NEXT:    [[SEL:%.*]] = select <2 x i1> [[COND]], <2 x float> <float 1.000000e+00, float poison>, <2 x float> [[X]]
+; CHECK-NEXT:    [[FREXP:%.*]] = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> [[SEL]])
+; CHECK-NEXT:    [[FREXP_0:%.*]] = extractvalue { <2 x float>, <2 x i32> } [[FREXP]], 0
+; CHECK-NEXT:    ret <2 x float> [[FREXP_0]]
+;
+  %sel = select <2 x i1> %cond, <2 x float> <float 1.000000e+00, float poison>, <2 x float> %x
+  %frexp = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> %sel)
+  %frexp.0 = extractvalue { <2 x float>, <2 x i32> } %frexp, 0
+  ret <2 x float> %frexp.0
+}
+
+; Vector test - non-splat (should not fold)
+define <2 x float> @test_select_frexp_vec_nonsplat(<2 x float> %x, <2 x i1> %cond) {
+; CHECK-LABEL: define <2 x float> @test_select_frexp_vec_nonsplat(
+; CHECK-SAME: <2 x float> [[X:%.*]], <2 x i1> [[COND:%.*]]) {
+; CHECK-NEXT:    [[SEL:%.*]] = select <2 x i1> [[COND]], <2 x float> <float 1.000000e+00, float 2.000000e+00>, <2 x float> [[X]]
+; CHECK-NEXT:    [[FREXP:%.*]] = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> [[SEL]])
+; CHECK-NEXT:    [[FREXP_0:%.*]] = extractvalue { <2 x float>, <2 x i32> } [[FREXP]], 0
+; CHECK-NEXT:    ret <2 x float> [[FREXP_0]]
+;
+  %sel = select <2 x i1> %cond, <2 x float> <float 1.000000e+00, float 2.000000e+00>, <2 x float> %x
+  %frexp = call { <2 x float>, <2 x i32> } @llvm.frexp.v2f32.v2i32(<2 x float> %sel)
+  %frexp.0 = extractvalue { <2 x float>, <2 x i32> } %frexp, 0
+  ret <2 x float> %frexp.0
+}
+
+; Negative test - both operands non-constant
+define float @test_select_frexp_no_const(float %x, float %y, i1 %cond) {
+; CHECK-LABEL: define float @test_select_frexp_no_const(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND]], float [[X]], float [[Y]]
+; CHECK-NEXT:    [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[SEL]])
+; CHECK-NEXT:    [[FREXP_0:%.*]] = extractvalue { float, i32 } [[FREXP]], 0
+; CHECK-NEXT:    ret float [[FREXP_0]]
+;
+  %sel = select i1 %cond, float %x, float %y
+  %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+  %frexp.0 = extractvalue { float, i32 } %frexp, 0
+  ret float %frexp.0
+}
+
+; Negative test - extracting exp instead of mantissa
+define i32 @test_select_frexp_extract_exp(float %x, i1 %cond) {
+; CHECK-LABEL: define i32 @test_select_frexp_extract_exp(
+; CHECK-SAME: float [[X:%.*]], i1 [[COND:%.*]]) {
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[COND]], float 1.000000e+00, float [[X]]
+; CHECK-NEXT:    [[FREXP:%.*]] = call { float, i32 } @llvm.frexp.f32.i32(float [[SEL]])
+; CHECK-NEXT:    [[FREXP_1:%.*]] = extractvalue { float, i32 } [[FREXP]], 1
+; CHECK-NEXT:    ret i32 [[FREXP_1]]
+;
+  %sel = select i1 %cond, float 1.000000e+00, float %x
+  %frexp = call { float, i32 } @llvm.frexp.f32.i32(float %sel)
+  %frexp.1 = extractvalue { float, i32 } %frexp, 1
+  ret i32 %frexp.1
+}
+
----------------
arsenm wrote:

Can you add some tests with fast math flags on the select to show the behavior? 

https://github.com/llvm/llvm-project/pull/121227