InstCombine: Add baseline test for #64697 fmul reassociation

[arsenm]

Currently fmul is not reassociated unless it has nsz, although
this should be unnecessary.

[arsenm]

• InstCombine: Fold ldexp with constant exponent to fmul #171731
• ValueTracking: Teach computeKnownFPClass that multiply can avoid denormals #171730
• ValueTracking: Add baseline test for fmul denormal scaling handling #171729
• IR: Stop requiring nsz to reassociate fmul #171726
• InstCombine: Add baseline test for #64697 fmul reassociation #171725 👈 (View in Graphite)
• main

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[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Matt Arsenault (arsenm)

Changes

Currently fmul is not reassociated unless it has nsz, although
this should be unnecessary.

---

Full diff: https://github.com/llvm/llvm-project/pull/171725.diff

1 Files Affected:

• (added) llvm/test/Transforms/InstCombine/issue64967-reassoc-fmul.ll (+117)

diff --git a/llvm/test/Transforms/InstCombine/issue64967-reassoc-fmul.ll b/llvm/test/Transforms/InstCombine/issue64967-reassoc-fmul.ll
new file mode 100644
index 0000000000000..16f9cf2dd64c5
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/issue64967-reassoc-fmul.ll
@@ -0,0 +1,117 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+; Show that unlike fadd, fmul does not require nsz to be reassociated.
+
+; Can't reassociate anyway
+define float @fmul(float %x) {
+; CHECK-LABEL: define float @fmul(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FMUL0:%.*]] = fmul float [[X]], 2.000000e+00
+; CHECK-NEXT:    [[FMUL1:%.*]] = fmul float [[FMUL0]], 4.000000e+00
+; CHECK-NEXT:    ret float [[FMUL1]]
+;
+  %fmul0 = fmul float %x, 2.0
+  %fmul1 = fmul float %fmul0, 4.0
+  ret float %fmul1
+}
+
+; Should be able to reassociate without nsz
+; (+0 * 2) * 4 = +0
+; (-0 * 2) * 4 = -0
+
+; (+0 * 8) = +0
+; (-0 * 8) = -0
+define float @fmul_reassoc(float %x) {
+; CHECK-LABEL: define float @fmul_reassoc(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FMUL0:%.*]] = fmul reassoc float [[X]], 2.000000e+00
+; CHECK-NEXT:    [[FMUL1:%.*]] = fmul reassoc float [[FMUL0]], 4.000000e+00
+; CHECK-NEXT:    ret float [[FMUL1]]
+;
+  %fmul0 = fmul reassoc float %x, 2.0
+  %fmul1 = fmul reassoc float %fmul0, 4.0
+  ret float %fmul1
+}
+
+define <2 x float> @fmul_reassoc_v2(<2 x float> %x) {
+; CHECK-LABEL: define <2 x float> @fmul_reassoc_v2(
+; CHECK-SAME: <2 x float> [[X:%.*]]) {
+; CHECK-NEXT:    [[FMUL0:%.*]] = fmul reassoc <2 x float> [[X]], splat (float 2.000000e+00)
+; CHECK-NEXT:    [[FMUL1:%.*]] = fmul reassoc <2 x float> [[FMUL0]], splat (float 4.000000e+00)
+; CHECK-NEXT:    ret <2 x float> [[FMUL1]]
+;
+  %fmul0 = fmul reassoc <2 x float> %x, splat (float 2.0)
+  %fmul1 = fmul reassoc <2 x float> %fmul0, splat (float 4.0)
+  ret <2 x float> %fmul1
+}
+
+; (+0 * 2) * -4 = -0
+; (-0 * 2) * -4 = +0
+
+; (+0 * -8) = -0
+; (-0 * -8) = +0
+define float @fmul_reassoc_negative_0(float %x) {
+; CHECK-LABEL: define float @fmul_reassoc_negative_0(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FMUL0:%.*]] = fmul reassoc float [[X]], 2.000000e+00
+; CHECK-NEXT:    [[FMUL1:%.*]] = fmul reassoc float [[FMUL0]], -4.000000e+00
+; CHECK-NEXT:    ret float [[FMUL1]]
+;
+  %fmul0 = fmul reassoc float %x, 2.0
+  %fmul1 = fmul reassoc float %fmul0, -4.0
+  ret float %fmul1
+}
+
+; (+0 * -2) * 4 = -0
+; (-0 * -2) * 4 = +0
+
+; (+0 * -8) = -0
+; (-0 * -8) = +0
+define float @fmul_reassoc_negative_1(float %x) {
+; CHECK-LABEL: define float @fmul_reassoc_negative_1(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FMUL0:%.*]] = fmul reassoc float [[X]], -2.000000e+00
+; CHECK-NEXT:    [[FMUL1:%.*]] = fmul reassoc float [[FMUL0]], 4.000000e+00
+; CHECK-NEXT:    ret float [[FMUL1]]
+;
+  %fmul0 = fmul reassoc float %x, -2.0
+  %fmul1 = fmul reassoc float %fmul0, 4.0
+  ret float %fmul1
+}
+
+; Does reassociate already, unnecessarily requires nsz on both multiplies.
+define float @fmul_reassoc_nsz(float %x) {
+; CHECK-LABEL: define float @fmul_reassoc_nsz(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FMUL1:%.*]] = fmul reassoc nsz float [[X]], 8.000000e+00
+; CHECK-NEXT:    ret float [[FMUL1]]
+;
+  %fmul0 = fmul nsz reassoc float %x, 2.0
+  %fmul1 = fmul nsz reassoc float %fmul0, 4.0
+  ret float %fmul1
+}
+
+define float @fmul_reassoc_posk_neg0(float %x) {
+; CHECK-LABEL: define float @fmul_reassoc_posk_neg0(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FMUL0:%.*]] = fmul reassoc float [[X]], 4.000000e+00
+; CHECK-NEXT:    [[FMUL1:%.*]] = fmul reassoc float [[FMUL0]], -0.000000e+00
+; CHECK-NEXT:    ret float [[FMUL1]]
+;
+  %fmul0 = fmul reassoc float %x, 4.0
+  %fmul1 = fmul reassoc float %fmul0, -0.0
+  ret float %fmul1
+}
+
+define float @fmul_reassoc_neg0_posk(float %x) {
+; CHECK-LABEL: define float @fmul_reassoc_neg0_posk(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FMUL0:%.*]] = fmul reassoc float [[X]], -0.000000e+00
+; CHECK-NEXT:    [[FMUL1:%.*]] = fmul reassoc float [[FMUL0]], 4.000000e+00
+; CHECK-NEXT:    ret float [[FMUL1]]
+;
+  %fmul0 = fmul reassoc float %x, -0.0
+  %fmul1 = fmul reassoc float %fmul0, 4.0
+  ret float %fmul1
+}

[andykaylor]

This looks good as a starting point for the fix.