[flang-commits] [lld] [libc] [clang-tools-extra] [lldb] [libcxxabi] [clang] [flang] [llvm] [SCEVExp] Keep NUW/NSW if both original inc and isomporphic inc agree. (PR #79512)

Florian Hahn via flang-commits flang-commits at lists.llvm.org
Thu Feb 1 01:40:58 PST 2024


https://github.com/fhahn updated https://github.com/llvm/llvm-project/pull/79512

>From 299a055e271264f918321bf7360ee37c6ede8b26 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Tue, 23 Jan 2024 13:39:38 +0000
Subject: [PATCH 1/2] [SCEVExp] Keep NUW/NSW if both original inc and
 isomporphic inc agree.

We are replacing with a wider increment. If both OrigInc and IsomorphicInc
are NUW/NSW, then we can preserve them on the wider increment; the narrower
IsomorphicInc would wrap before the wider OrigInc, so the replacement won't
make IsomorphicInc's uses more poisonous.
---
 .../Utils/ScalarEvolutionExpander.cpp         | 28 +++++++++++++++++--
 .../Transforms/IndVarSimplify/iv-poison.ll    | 12 ++++----
 2 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index cf8cea937a6bf..902c4db883769 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -1607,11 +1607,35 @@ void SCEVExpander::replaceCongruentIVInc(
   const SCEV *TruncExpr =
       SE.getTruncateOrNoop(SE.getSCEV(OrigInc), IsomorphicInc->getType());
   if (OrigInc == IsomorphicInc || TruncExpr != SE.getSCEV(IsomorphicInc) ||
-      !SE.LI.replacementPreservesLCSSAForm(IsomorphicInc, OrigInc) ||
-      !hoistIVInc(OrigInc, IsomorphicInc,
+      !SE.LI.replacementPreservesLCSSAForm(IsomorphicInc, OrigInc))
+    return;
+
+  bool BothHaveNUW = false;
+  bool BothHaveNSW = false;
+  auto *OBOIncV = dyn_cast<OverflowingBinaryOperator>(OrigInc);
+  auto *OBOIsomorphic = dyn_cast<OverflowingBinaryOperator>(IsomorphicInc);
+  assert(OrigInc->getType()->getScalarSizeInBits() >=
+         IsomorphicInc->getType()->getScalarSizeInBits()) && "Should only replace an increment with a wider one.");
+  if (OBOIncV && OBOIsomorphic) {
+    BothHaveNUW =
+        OBOIncV->hasNoUnsignedWrap() && OBOIsomorphic->hasNoUnsignedWrap();
+    BothHaveNSW =
+        OBOIncV->hasNoSignedWrap() && OBOIsomorphic->hasNoSignedWrap();
+  }
+
+  if (!hoistIVInc(OrigInc, IsomorphicInc,
                   /*RecomputePoisonFlags*/ true))
     return;
 
+  // We are replacing with a wider increment. If both OrigInc and IsomorphicInc
+  // are NUW/NSW, then we can preserve them on the wider increment; the narrower
+  // IsomorphicInc would wrap before the wider OrigInc, so the replacement won't
+  // make IsomorphicInc's uses more poisonous.
+  if (BothHaveNUW || BothHaveNSW) {
+    OrigInc->setHasNoUnsignedWrap(OBOIncV->hasNoUnsignedWrap() || BothHaveNUW);
+    OrigInc->setHasNoSignedWrap(OBOIncV->hasNoSignedWrap() || BothHaveNSW);
+  }
+
   SCEV_DEBUG_WITH_TYPE(DebugType,
                        dbgs() << "INDVARS: Eliminated congruent iv.inc: "
                               << *IsomorphicInc << '\n');
diff --git a/llvm/test/Transforms/IndVarSimplify/iv-poison.ll b/llvm/test/Transforms/IndVarSimplify/iv-poison.ll
index 38299e0a6b353..383599f614357 100644
--- a/llvm/test/Transforms/IndVarSimplify/iv-poison.ll
+++ b/llvm/test/Transforms/IndVarSimplify/iv-poison.ll
@@ -64,7 +64,7 @@ define i2 @iv_hoist_both_adds_nsw(i2 %arg) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV_0:%.*]] = phi i2 [ 1, [[BB:%.*]] ], [ [[IV_0_NEXT:%.*]], [[LOOP]] ]
-; CHECK-NEXT:    [[IV_0_NEXT]] = add nuw i2 [[IV_0]], 1
+; CHECK-NEXT:    [[IV_0_NEXT]] = add nuw nsw i2 [[IV_0]], 1
 ; CHECK-NEXT:    [[DOTNOT_NOT:%.*]] = icmp ult i2 1, [[ARG:%.*]]
 ; CHECK-NEXT:    br i1 [[DOTNOT_NOT]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
@@ -92,7 +92,7 @@ define i4 @iv_hoist_both_adds_nsw_extra_use(i4 %arg) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV_0:%.*]] = phi i4 [ 1, [[BB:%.*]] ], [ [[IV_0_NEXT:%.*]], [[LOOP]] ]
-; CHECK-NEXT:    [[IV_0_NEXT]] = add nuw i4 [[IV_0]], 1
+; CHECK-NEXT:    [[IV_0_NEXT]] = add nuw nsw i4 [[IV_0]], 1
 ; CHECK-NEXT:    call void @use(i4 [[IV_0_NEXT]])
 ; CHECK-NEXT:    call void @use(i4 [[IV_0_NEXT]])
 ; CHECK-NEXT:    [[DOTNOT_NOT:%.*]] = icmp ult i4 1, [[ARG:%.*]]
@@ -124,7 +124,7 @@ define i4 @iv_hoist_both_adds_nsw_extra_use_incs_reordered(i4 %arg) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV_0:%.*]] = phi i4 [ 1, [[BB:%.*]] ], [ [[IV_0_NEXT:%.*]], [[LOOP]] ]
-; CHECK-NEXT:    [[IV_0_NEXT]] = add nuw i4 [[IV_0]], 1
+; CHECK-NEXT:    [[IV_0_NEXT]] = add nuw nsw i4 [[IV_0]], 1
 ; CHECK-NEXT:    call void @use(i4 [[IV_0_NEXT]])
 ; CHECK-NEXT:    call void @use(i4 [[IV_0_NEXT]])
 ; CHECK-NEXT:    [[DOTNOT_NOT:%.*]] = icmp ult i4 1, [[ARG:%.*]]
@@ -244,7 +244,7 @@ define i2 @iv_hoist_both_adds_nuw(i2 %arg, i2 %start) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV_0:%.*]] = phi i2 [ [[START:%.*]], [[BB:%.*]] ], [ [[IV_0_NEXT:%.*]], [[LOOP]] ]
-; CHECK-NEXT:    [[IV_0_NEXT]] = add i2 [[IV_0]], 1
+; CHECK-NEXT:    [[IV_0_NEXT]] = add nuw i2 [[IV_0]], 1
 ; CHECK-NEXT:    [[DOTNOT_NOT:%.*]] = icmp ult i2 [[START]], [[ARG:%.*]]
 ; CHECK-NEXT:    br i1 [[DOTNOT_NOT]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
@@ -272,7 +272,7 @@ define i4 @iv_hoist_both_adds_nuw_extra_use(i4 %arg, i4 %start) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV_0:%.*]] = phi i4 [ [[START:%.*]], [[BB:%.*]] ], [ [[IV_0_NEXT:%.*]], [[LOOP]] ]
-; CHECK-NEXT:    [[IV_0_NEXT]] = add i4 [[IV_0]], 1
+; CHECK-NEXT:    [[IV_0_NEXT]] = add nuw i4 [[IV_0]], 1
 ; CHECK-NEXT:    call void @use(i4 [[IV_0_NEXT]])
 ; CHECK-NEXT:    call void @use(i4 [[IV_0_NEXT]])
 ; CHECK-NEXT:    [[DOTNOT_NOT:%.*]] = icmp ult i4 [[START]], [[ARG:%.*]]
@@ -304,7 +304,7 @@ define i4 @iv_hoist_both_adds_nuw_extra_use_incs_reordered(i4 %arg, i4 %start) {
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV_0:%.*]] = phi i4 [ [[START:%.*]], [[BB:%.*]] ], [ [[IV_0_NEXT:%.*]], [[LOOP]] ]
-; CHECK-NEXT:    [[IV_0_NEXT]] = add i4 [[IV_0]], 1
+; CHECK-NEXT:    [[IV_0_NEXT]] = add nuw i4 [[IV_0]], 1
 ; CHECK-NEXT:    call void @use(i4 [[IV_0_NEXT]])
 ; CHECK-NEXT:    call void @use(i4 [[IV_0_NEXT]])
 ; CHECK-NEXT:    [[DOTNOT_NOT:%.*]] = icmp ult i4 [[START]], [[ARG:%.*]]

>From d75c570c47b1463d9c677ed9f295ed7aaae17b60 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Thu, 1 Feb 2024 09:39:56 +0000
Subject: [PATCH 2/2] !fixup remove extra ) from assert, move to comment.

---
 llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index e2e086b2a17b8..ed55a13072aaa 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -1611,8 +1611,6 @@ void SCEVExpander::replaceCongruentIVInc(
   bool BothHaveNSW = false;
   auto *OBOIncV = dyn_cast<OverflowingBinaryOperator>(OrigInc);
   auto *OBOIsomorphic = dyn_cast<OverflowingBinaryOperator>(IsomorphicInc);
-  assert(OrigInc->getType()->getScalarSizeInBits() >=
-         IsomorphicInc->getType()->getScalarSizeInBits()) && "Should only replace an increment with a wider one.");
   if (OBOIncV && OBOIsomorphic) {
     BothHaveNUW =
         OBOIncV->hasNoUnsignedWrap() && OBOIsomorphic->hasNoUnsignedWrap();
@@ -1628,6 +1626,9 @@ void SCEVExpander::replaceCongruentIVInc(
   // are NUW/NSW, then we can preserve them on the wider increment; the narrower
   // IsomorphicInc would wrap before the wider OrigInc, so the replacement won't
   // make IsomorphicInc's uses more poisonous.
+  assert(OrigInc->getType()->getScalarSizeInBits() >=
+             IsomorphicInc->getType()->getScalarSizeInBits() &&
+         "Should only replace an increment with a wider one.");
   if (BothHaveNUW || BothHaveNSW) {
     OrigInc->setHasNoUnsignedWrap(OBOIncV->hasNoUnsignedWrap() || BothHaveNUW);
     OrigInc->setHasNoSignedWrap(OBOIncV->hasNoSignedWrap() || BothHaveNSW);



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