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9baaae9344
Fixes PR27315.
The post-inc version of an add recurrence needs to "follow the same
rules" as a normal add or subtract expression. Otherwise we miscompile
programs like
```
int main() {
int a = 0;
unsigned a_u = 0;
volatile long last_value;
do {
a_u += 3;
last_value = (long) ((int) a_u);
if (will_add_overflow(a, 3)) {
// Leave, and don't actually do the increment, so no UB.
printf("last_value = %ld\n", last_value);
exit(0);
}
a += 3;
} while (a != 46);
return 0;
}
```
This patch changes SCEV to put no-wrap flags on post-inc add recurrences
only when the poison from a potential overflow will go ahead to cause
undefined behavior.
To avoid regressing performance too much, I've assumed infinite loops
without side effects is undefined behavior to prove poison<->UB
equivalence in more cases. This isn't ideal, but is not new to LLVM as
a whole, and far better than the situation I'm trying to fix.
llvm-svn: 271151
110 lines
3.2 KiB
LLVM
110 lines
3.2 KiB
LLVM
; ; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
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define void @infer.sext.0(i1* %c, i32 %start, i32* %buf) {
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; CHECK-LABEL: Classifying expressions for: @infer.sext.0
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entry:
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br label %loop
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loop:
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%counter = phi i32 [ 0, %entry ], [ %counter.inc, %loop ]
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%idx = phi i32 [ %start, %entry ], [ %idx.inc, %loop ]
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%idx.inc = add nsw i32 %idx, 1
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%idx.inc.sext = sext i32 %idx.inc to i64
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; CHECK: %idx.inc.sext = sext i32 %idx.inc to i64
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; CHECK-NEXT: --> {(1 + (sext i32 %start to i64))<nsw>,+,1}<nsw><%loop>
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%buf.gep = getelementptr inbounds i32, i32* %buf, i32 %idx.inc
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%val = load i32, i32* %buf.gep
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%condition = icmp eq i32 %counter, 1
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%counter.inc = add i32 %counter, 1
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br i1 %condition, label %exit, label %loop
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exit:
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ret void
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}
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define void @infer.zext.0(i1* %c, i32 %start, i32* %buf) {
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; CHECK-LABEL: Classifying expressions for: @infer.zext.0
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entry:
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br label %loop
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loop:
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%counter = phi i32 [ 0, %entry ], [ %counter.inc, %loop ]
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%idx = phi i32 [ %start, %entry ], [ %idx.inc, %loop ]
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%idx.inc = add nuw i32 %idx, 1
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%idx.inc.sext = zext i32 %idx.inc to i64
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; CHECK: %idx.inc.sext = zext i32 %idx.inc to i64
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; CHECK-NEXT: --> {(1 + (zext i32 %start to i64))<nuw><nsw>,+,1}<nuw><%loop>
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%buf.gep = getelementptr inbounds i32, i32* %buf, i32 %idx.inc
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%val = load i32, i32* %buf.gep
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%condition = icmp eq i32 %counter, 1
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%counter.inc = add i32 %counter, 1
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br i1 %condition, label %exit, label %loop
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exit:
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ret void
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}
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define void @infer.sext.1(i32 %start, i1* %c) {
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; CHECK-LABEL: Classifying expressions for: @infer.sext.1
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entry:
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%start.mul = mul i32 %start, 4
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%start.real = add i32 %start.mul, 2
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br label %loop
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loop:
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%idx = phi i32 [ %start.real, %entry ], [ %idx.inc, %loop ]
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%idx.sext = sext i32 %idx to i64
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; CHECK: %idx.sext = sext i32 %idx to i64
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; CHECK-NEXT: --> {(2 + (sext i32 (4 * %start) to i64))<nsw>,+,2}<nsw><%loop>
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%idx.inc = add nsw i32 %idx, 2
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%condition = load i1, i1* %c
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br i1 %condition, label %exit, label %loop
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exit:
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ret void
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}
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define void @infer.sext.2(i1* %c, i8 %start) {
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; CHECK-LABEL: Classifying expressions for: @infer.sext.2
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entry:
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%start.inc = add i8 %start, 1
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%entry.condition = icmp slt i8 %start, 127
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br i1 %entry.condition, label %loop, label %exit
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loop:
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%idx = phi i8 [ %start.inc, %entry ], [ %idx.inc, %loop ]
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%idx.sext = sext i8 %idx to i16
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; CHECK: %idx.sext = sext i8 %idx to i16
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; CHECK-NEXT: --> {(1 + (sext i8 %start to i16))<nsw>,+,1}<nsw><%loop>
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%idx.inc = add nsw i8 %idx, 1
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%condition = load volatile i1, i1* %c
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br i1 %condition, label %exit, label %loop
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exit:
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ret void
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}
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define void @infer.zext.1(i1* %c, i8 %start) {
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; CHECK-LABEL: Classifying expressions for: @infer.zext.1
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entry:
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%start.inc = add i8 %start, 1
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%entry.condition = icmp ult i8 %start, 255
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br i1 %entry.condition, label %loop, label %exit
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loop:
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%idx = phi i8 [ %start.inc, %entry ], [ %idx.inc, %loop ]
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%idx.zext = zext i8 %idx to i16
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; CHECK: %idx.zext = zext i8 %idx to i16
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; CHECK-NEXT: --> {(1 + (zext i8 %start to i16))<nuw><nsw>,+,1}<nuw><%loop>
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%idx.inc = add nuw i8 %idx, 1
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%condition = load volatile i1, i1* %c
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br i1 %condition, label %exit, label %loop
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exit:
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ret void
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}
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