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[SCEV] Fix sext handling for getConstantMultiple (#117093)

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Counterexample: 219 is a multiple of 73. But `sext i8 219 to i16 =
65499` is not.
Fixes https://github.com/llvm/llvm-project/issues/116483.

(cherry picked from commit 458dfbd855806461b4508bf8845cafe0411dbfd4)
This commit is contained in:
Yingwei Zheng 2024-11-21 17:23:04 +08:00 committed by Tobias Hieta
parent 336f87753b
commit 11be11b877
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3 changed files with 65 additions and 1 deletions
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4
llvm/lib/Analysis/ScalarEvolution.cpp
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@ -6313,8 +6313,10 @@ APInt ScalarEvolution::getConstantMultipleImpl(const SCEV *S) {
return getConstantMultiple(Z->getOperand()).zext(BitWidth);
}
case scSignExtend: {
// Only multiples that are a power of 2 will hold after sext.
const SCEVSignExtendExpr *E = cast<SCEVSignExtendExpr>(S);
return getConstantMultiple(E->getOperand()).sext(BitWidth);
uint32_t TZ = getMinTrailingZeros(E->getOperand());
return GetShiftedByZeros(TZ);
}
case scMulExpr: {
const SCEVMulExpr *M = cast<SCEVMulExpr>(S);

26
llvm/test/Analysis/ScalarEvolution/pr116483.ll Normal file
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@ -0,0 +1,26 @@
; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 5
; RUN: opt -S -disable-output "-passes=print<scalar-evolution>" < %s 2>&1 | FileCheck %s
define i16 @test() {
; CHECK-LABEL: 'test'
; CHECK-NEXT: Classifying expressions for: @test
; CHECK-NEXT: %xor = xor i32 0, 3
; CHECK-NEXT: --> %xor U: [3,4) S: [3,4)
; CHECK-NEXT: %mul = mul i32 %xor, 329
; CHECK-NEXT: --> (329 * %xor)<nuw><nsw> U: [987,988) S: [987,988)
; CHECK-NEXT: %conv = trunc i32 %mul to i16
; CHECK-NEXT: --> (329 * (trunc i32 %xor to i16))<nuw><nsw> U: [987,988) S: [987,988)
; CHECK-NEXT: %sext = shl i16 %conv, 8
; CHECK-NEXT: --> (18688 * (trunc i32 %xor to i16))<nuw> U: [-9472,-9471) S: [-9472,-9471)
; CHECK-NEXT: %conv1 = ashr i16 %sext, 8
; CHECK-NEXT: --> (sext i8 (73 * (trunc i32 %xor to i8))<nuw> to i16) U: [-37,-36) S: [-37,-36)
; CHECK-NEXT: Determining loop execution counts for: @test
;
entry:
%xor = xor i32 0, 3
%mul = mul i32 %xor, 329
%conv = trunc i32 %mul to i16
%sext = shl i16 %conv, 8
%conv1 = ashr i16 %sext, 8
ret i16 %conv1
}

36
llvm/test/Transforms/IndVarSimplify/pr116483.ll Normal file
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@ -0,0 +1,36 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -S -passes=indvars < %s | FileCheck %s
define i32 @test() {
; CHECK-LABEL: define i32 @test() {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[XOR:%.*]] = xor i32 0, 3
; CHECK-NEXT: [[MUL:%.*]] = mul i32 [[XOR]], 329
; CHECK-NEXT: [[CONV:%.*]] = trunc i32 [[MUL]] to i16
; CHECK-NEXT: [[SEXT:%.*]] = shl i16 [[CONV]], 8
; CHECK-NEXT: [[CONV1:%.*]] = ashr i16 [[SEXT]], 8
; CHECK-NEXT: br label %[[LOOP_BODY:.*]]
; CHECK: [[LOOP_BODY]]:
; CHECK-NEXT: br i1 true, label %[[EXIT:.*]], label %[[LOOP_BODY]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: [[CONV3:%.*]] = zext i16 [[CONV1]] to i32
; CHECK-NEXT: ret i32 [[CONV3]]
;
entry:
%xor = xor i32 0, 3
%mul = mul i32 %xor, 329
%conv = trunc i32 %mul to i16
%sext = shl i16 %conv, 8
%conv1 = ashr i16 %sext, 8
%conv3 = zext i16 %conv1 to i32
br label %loop.body
loop.body:
%indvar = phi i32 [ %indvar.inc, %loop.body ], [ 1, %entry ]
%indvar.inc = add nuw i32 %indvar, 1
%exitcond = icmp eq i32 %indvar, %conv3
br i1 %exitcond, label %exit, label %loop.body
exit:
ret i32 %conv3
}