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[LoopUnroll] Fix truncation bug in canUnrollCompletely.

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Summary:
canUnrollCompletely takes `unsigned` values for `UnrolledCost` and
`RolledDynamicCost` but is passed in `uint64_t`s that are silently
truncated.  Because of this, when `UnrolledSize` is a large integer
that has a small remainder with UINT32_MAX, LLVM tries to completely
unroll loops with high trip counts.

Reviewers: mzolotukhin, chandlerc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10293

llvm-svn: 239218
This commit is contained in:
Sanjoy Das 2015-06-06 05:24:10 +00:00
parent 212ab571c4
commit 7dbb3087e2
2 changed files with 61 additions and 3 deletions
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6
lib/Transforms/Scalar/LoopUnrollPass.cpp
View File

@ -227,7 +227,7 @@ namespace {
bool canUnrollCompletely(Loop *L, unsigned Threshold,
unsigned PercentDynamicCostSavedThreshold,
unsigned DynamicCostSavingsDiscount,
unsigned UnrolledCost, unsigned RolledDynamicCost);
uint64_t UnrolledCost, uint64_t RolledDynamicCost);
};
}
@ -768,8 +768,8 @@ static void SetLoopAlreadyUnrolled(Loop *L) {
bool LoopUnroll::canUnrollCompletely(Loop *L, unsigned Threshold,
unsigned PercentDynamicCostSavedThreshold,
unsigned DynamicCostSavingsDiscount,
unsigned UnrolledCost,
unsigned RolledDynamicCost) {
uint64_t UnrolledCost,
uint64_t RolledDynamicCost) {
if (Threshold == NoThreshold) {
DEBUG(dbgs() << " Can fully unroll, because no threshold is set.\n");

58
test/Transforms/LoopUnroll/full-unroll-bad-cost.ll Normal file
View File

@ -0,0 +1,58 @@
; RUN: opt -S -loop-unroll < %s | FileCheck %s
; LLVM should not try to fully unroll this loop.
declare void @f()
declare void @g()
declare void @h()
define void @trivial_loop() {
; CHECK-LABEL: @trivial_loop(
entry:
br label %loop
loop:
%idx = phi i32 [ 0, %entry ], [ %idx.inc, %loop ]
%idx.inc = add i32 %idx, 1
call void @f()
call void @g()
call void @h()
call void @f()
call void @g()
call void @h()
call void @f()
call void @g()
call void @h()
call void @f()
call void @g()
call void @h()
call void @f()
call void @g()
call void @h()
%be = icmp slt i32 %idx, 268435456
br i1 %be, label %loop, label %exit
; CHECK: loop:
; CHECK-NEXT: %idx = phi i32 [ 0, %entry ], [ %idx.inc, %loop ]
; CHECK-NEXT: %idx.inc = add i32 %idx, 1
; CHECK-NEXT: call void @f()
; CHECK-NEXT: call void @g()
; CHECK-NEXT: call void @h()
; CHECK-NEXT: call void @f()
; CHECK-NEXT: call void @g()
; CHECK-NEXT: call void @h()
; CHECK-NEXT: call void @f()
; CHECK-NEXT: call void @g()
; CHECK-NEXT: call void @h()
; CHECK-NEXT: call void @f()
; CHECK-NEXT: call void @g()
; CHECK-NEXT: call void @h()
; CHECK-NEXT: call void @f()
; CHECK-NEXT: call void @g()
; CHECK-NEXT: call void @h()
; CHECK-NEXT: %be = icmp slt i32 %idx, 268435456
; CHECK-NEXT: br i1 %be, label %loop, label %exit
exit:
ret void
}