[llvm] Reland "[InstCombine] Fold (sub nuw X, (Y << nuw Z)) >>u exact Z --> (X >>u exact Z) sub nuw Y" (PR #93571)

via llvm-commits llvm-commits at lists.llvm.org
Thu May 30 04:31:25 PDT 2024


https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/93571

>From 75dd3f065e28699bde08d490fd65212c82c21080 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Tue, 7 May 2024 15:29:07 -0400
Subject: [PATCH 1/2] [InstCombine] Pre-commit tests (NFC)

---
 llvm/test/Transforms/InstCombine/lshr.ll | 116 +++++++++++++++++++++++
 1 file changed, 116 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/lshr.ll b/llvm/test/Transforms/InstCombine/lshr.ll
index 0392764490945..fc4ff87c2aa8b 100644
--- a/llvm/test/Transforms/InstCombine/lshr.ll
+++ b/llvm/test/Transforms/InstCombine/lshr.ll
@@ -464,6 +464,122 @@ define i32 @shl_sub_lshr(i32 %x, i32 %c, i32 %y) {
   ret i32 %lshr
 }
 
+define i32 @shl_sub_lshr_reverse(i32 %x, i32 %c, i32 %y) {
+; CHECK-LABEL: @shl_sub_lshr_reverse(
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub nuw nsw i32 [[Y:%.*]], [[SHL]]
+; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    ret i32 [[LSHR]]
+;
+  %shl = shl nuw i32 %x, %c
+  %sub = sub nuw nsw i32 %y, %shl
+  %lshr = lshr exact i32 %sub, %c
+  ret i32 %lshr
+}
+
+define i32 @shl_sub_lshr_reverse_no_nsw(i32 %x, i32 %c, i32 %y) {
+; CHECK-LABEL: @shl_sub_lshr_reverse_no_nsw(
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
+; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    ret i32 [[LSHR]]
+;
+  %shl = shl nuw i32 %x, %c
+  %sub = sub nuw i32 %y, %shl
+  %lshr = lshr exact i32 %sub, %c
+  ret i32 %lshr
+}
+
+define i32 @shl_sub_lshr_reverse_nsw_on_op1(i32 %x, i32 %c, i32 %y) {
+; CHECK-LABEL: @shl_sub_lshr_reverse_nsw_on_op1(
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw nsw i32 [[X:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
+; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    ret i32 [[LSHR]]
+;
+  %shl = shl nuw nsw i32 %x, %c
+  %sub = sub nuw i32 %y, %shl
+  %lshr = lshr exact i32 %sub, %c
+  ret i32 %lshr
+}
+
+; Negative test
+
+define i32 @shl_sub_lshr_reverse_no_exact(i32 %x, i32 %c, i32 %y) {
+; CHECK-LABEL: @shl_sub_lshr_reverse_no_exact(
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub nuw nsw i32 [[Y:%.*]], [[SHL]]
+; CHECK-NEXT:    [[LSHR:%.*]] = lshr i32 [[SUB]], [[C]]
+; CHECK-NEXT:    ret i32 [[LSHR]]
+;
+  %shl = shl nuw i32 %x, %c
+  %sub = sub nuw nsw i32 %y, %shl
+  %lshr = lshr i32 %sub, %c
+  ret i32 %lshr
+}
+
+; Negative test
+
+define i32 @shl_sub_lshr_reverse_multiuse(i32 %x, i32 %c, i32 %y) {
+; CHECK-LABEL: @shl_sub_lshr_reverse_multiuse(
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
+; CHECK-NEXT:    call void @use(i32 [[SUB]])
+; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    ret i32 [[LSHR]]
+;
+  %shl = shl nuw i32 %x, %c
+  %sub = sub nuw i32 %y, %shl
+  call void @use(i32 %sub)
+  %lshr = lshr exact i32 %sub, %c
+  ret i32 %lshr
+}
+
+define i32 @shl_sub_lshr_reverse_multiuse2(i32 %x, i32 %c, i32 %y) {
+; CHECK-LABEL: @shl_sub_lshr_reverse_multiuse2(
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
+; CHECK-NEXT:    call void @use(i32 [[SHL]])
+; CHECK-NEXT:    [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
+; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    ret i32 [[LSHR]]
+;
+  %shl = shl nuw i32 %x, %c
+  call void @use(i32 %shl)
+  %sub = sub nuw i32 %y, %shl
+  %lshr = lshr exact i32 %sub, %c
+  ret i32 %lshr
+}
+
+; Negative test
+
+define i32 @shl_sub_lshr_reverse_no_nuw(i32 %x, i32 %c, i32 %y) {
+; CHECK-LABEL: @shl_sub_lshr_reverse_no_nuw(
+; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[X:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
+; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    ret i32 [[LSHR]]
+;
+  %shl = shl i32 %x, %c
+  %sub = sub nuw i32 %y, %shl
+  %lshr = lshr exact i32 %sub, %c
+  ret i32 %lshr
+}
+
+; Negative test
+
+define i32 @shl_sub_lshr_reverse_no_nsw_2(i32 %x, i32 %c, i32 %y) {
+; CHECK-LABEL: @shl_sub_lshr_reverse_no_nsw_2(
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw nsw i32 [[X:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub i32 [[Y:%.*]], [[SHL]]
+; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    ret i32 [[LSHR]]
+;
+  %shl = shl nuw nsw i32 %x, %c
+  %sub = sub i32 %y, %shl
+  %lshr = lshr exact i32 %sub, %c
+  ret i32 %lshr
+}
+
 define i32 @shl_or_lshr(i32 %x, i32 %c, i32 %y) {
 ; CHECK-LABEL: @shl_or_lshr(
 ; CHECK-NEXT:    [[TMP1:%.*]] = lshr i32 [[Y:%.*]], [[C:%.*]]

>From 23de287395d62c22fc6a14e2c34fea3b47d9b914 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Tue, 7 May 2024 15:30:01 -0400
Subject: [PATCH 2/2] [InstCombine] Fold (sub nuw X, (Y << nuw Z)) >>u exact Z
 --> (X >>u exact Z) sub nuw Y

This is the same fold as ((X << nuw Z) sub nuw Y) >>u exact Z --> X sub nuw (Y >>u exact Z), but with the sub operands swapped.

Alive2 Proof:
https://alive2.llvm.org/ce/z/2cRcdx
---
 .../InstCombine/InstCombineShifts.cpp         | 11 +++++++++++
 llvm/test/Transforms/InstCombine/lshr.ll      | 19 ++++++++-----------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index fbc02cddfb005..9ff817da79368 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -1275,6 +1275,17 @@ Instruction *InstCombinerImpl::visitLShr(BinaryOperator &I) {
     return NewSub;
   }
 
+  // (sub nuw X, (Y << nuw Z)) >>u exact Z --> (X >>u exact Z) sub nuw Y
+  if (I.isExact() &&
+      match(Op0, m_OneUse(m_NUWSub(m_Value(X),
+                                   m_NUWShl(m_Value(Y), m_Specific(Op1)))))) {
+    Value *NewLshr = Builder.CreateLShr(X, Op1, "", /*isExact=*/true);
+    auto *NewSub = BinaryOperator::CreateNUWSub(NewLshr, Y);
+    NewSub->setHasNoSignedWrap(
+        cast<OverflowingBinaryOperator>(Op0)->hasNoSignedWrap());
+    return NewSub;
+  }
+
   auto isSuitableBinOpcode = [](Instruction::BinaryOps BinOpcode) {
     switch (BinOpcode) {
     default:
diff --git a/llvm/test/Transforms/InstCombine/lshr.ll b/llvm/test/Transforms/InstCombine/lshr.ll
index fc4ff87c2aa8b..60f03733ebd99 100644
--- a/llvm/test/Transforms/InstCombine/lshr.ll
+++ b/llvm/test/Transforms/InstCombine/lshr.ll
@@ -466,9 +466,8 @@ define i32 @shl_sub_lshr(i32 %x, i32 %c, i32 %y) {
 
 define i32 @shl_sub_lshr_reverse(i32 %x, i32 %c, i32 %y) {
 ; CHECK-LABEL: @shl_sub_lshr_reverse(
-; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
-; CHECK-NEXT:    [[SUB:%.*]] = sub nuw nsw i32 [[Y:%.*]], [[SHL]]
-; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr exact i32 [[Y:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[LSHR:%.*]] = sub nuw nsw i32 [[TMP1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[LSHR]]
 ;
   %shl = shl nuw i32 %x, %c
@@ -479,9 +478,8 @@ define i32 @shl_sub_lshr_reverse(i32 %x, i32 %c, i32 %y) {
 
 define i32 @shl_sub_lshr_reverse_no_nsw(i32 %x, i32 %c, i32 %y) {
 ; CHECK-LABEL: @shl_sub_lshr_reverse_no_nsw(
-; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
-; CHECK-NEXT:    [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
-; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr exact i32 [[Y:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[LSHR:%.*]] = sub nuw i32 [[TMP1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[LSHR]]
 ;
   %shl = shl nuw i32 %x, %c
@@ -492,9 +490,8 @@ define i32 @shl_sub_lshr_reverse_no_nsw(i32 %x, i32 %c, i32 %y) {
 
 define i32 @shl_sub_lshr_reverse_nsw_on_op1(i32 %x, i32 %c, i32 %y) {
 ; CHECK-LABEL: @shl_sub_lshr_reverse_nsw_on_op1(
-; CHECK-NEXT:    [[SHL:%.*]] = shl nuw nsw i32 [[X:%.*]], [[C:%.*]]
-; CHECK-NEXT:    [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
-; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr exact i32 [[Y:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[LSHR:%.*]] = sub nuw i32 [[TMP1]], [[X:%.*]]
 ; CHECK-NEXT:    ret i32 [[LSHR]]
 ;
   %shl = shl nuw nsw i32 %x, %c
@@ -539,8 +536,8 @@ define i32 @shl_sub_lshr_reverse_multiuse2(i32 %x, i32 %c, i32 %y) {
 ; CHECK-LABEL: @shl_sub_lshr_reverse_multiuse2(
 ; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i32 [[X:%.*]], [[C:%.*]]
 ; CHECK-NEXT:    call void @use(i32 [[SHL]])
-; CHECK-NEXT:    [[SUB:%.*]] = sub nuw i32 [[Y:%.*]], [[SHL]]
-; CHECK-NEXT:    [[LSHR:%.*]] = lshr exact i32 [[SUB]], [[C]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr exact i32 [[Y:%.*]], [[C]]
+; CHECK-NEXT:    [[LSHR:%.*]] = sub nuw i32 [[TMP1]], [[X]]
 ; CHECK-NEXT:    ret i32 [[LSHR]]
 ;
   %shl = shl nuw i32 %x, %c



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