2cdc6f2ca6
When doing load/store promotion within LICM, if we
cannot prove that it is safe to sink the store we won't
hoist the load, even though we can prove the load could
be dereferenced and moved outside the loop. This patch
implements the load promotion by moving it in the loop
preheader by inserting proper PHI in the loop. The store
is kept as is in the loop. By doing this, we avoid doing
the load from a memory location in each iteration.
Please consider this small example:
loop {
var = *ptr;
if (var) break;
*ptr= var + 1;
}
After this patch, it will be:
var0 = *ptr;
loop {
var1 = phi (var0, var2);
if (var1) break;
var2 = var1 + 1;
*ptr = var2;
}
This addresses some problems from [0].
[0] https://bugs.llvm.org/show_bug.cgi?id=51193
Differential revision: https://reviews.llvm.org/D113289
107 lines
3.3 KiB
LLVM
107 lines
3.3 KiB
LLVM
; ModuleID = 'bug.c'
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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; RUN: opt -O2 -S < %s | FileCheck %s
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; CHECK-LABEL: main
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; CHECK: memset
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; CHECK: if.then
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; CHECK: store
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; CHECK: if.end
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; CHECK: store
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; CHECK: store
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@d = common global i32 0, align 4
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@b = common global i32 0, align 4
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@f = common global [1 x [3 x i8]] zeroinitializer, align 1
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@e = common global i32 0, align 4
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@c = common global i32 0, align 4
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@a = common global i32 0, align 4
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; Function Attrs: nounwind uwtable
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define void @fn1() {
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entry:
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store i32 0, i32* @d, align 4
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br label %for.cond
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for.cond: ; preds = %for.inc8, %entry
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%0 = load i32, i32* @d, align 4
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%cmp = icmp slt i32 %0, 2
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br i1 %cmp, label %for.body, label %for.end10
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for.body: ; preds = %for.cond
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%1 = load i32, i32* @d, align 4
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%idxprom = sext i32 %1 to i64
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%2 = load i32, i32* @b, align 4
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%idxprom1 = sext i32 %2 to i64
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%arrayidx = getelementptr inbounds [1 x [3 x i8]], [1 x [3 x i8]]* @f, i32 0, i64 %idxprom1
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%arrayidx2 = getelementptr inbounds [3 x i8], [3 x i8]* %arrayidx, i32 0, i64 %idxprom
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store i8 0, i8* %arrayidx2, align 1
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store i32 0, i32* @e, align 4
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br label %for.cond3
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for.cond3: ; preds = %for.inc, %for.body
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%3 = load i32, i32* @e, align 4
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%cmp4 = icmp slt i32 %3, 3
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br i1 %cmp4, label %for.body5, label %for.end
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for.body5: ; preds = %for.cond3
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%4 = load i32, i32* @c, align 4
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%tobool = icmp ne i32 %4, 0
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br i1 %tobool, label %if.then, label %if.end
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if.then: ; preds = %for.body5
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%5 = load i32, i32* @a, align 4
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%dec = add nsw i32 %5, -1
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store i32 %dec, i32* @a, align 4
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br label %if.end
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if.end: ; preds = %if.then, %for.body5
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%6 = load i32, i32* @e, align 4
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%idxprom6 = sext i32 %6 to i64
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%arrayidx7 = getelementptr inbounds [3 x i8], [3 x i8]* getelementptr inbounds ([1 x [3 x i8]], [1 x [3 x i8]]* @f, i32 0, i64 0), i32 0, i64 %idxprom6
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store i8 1, i8* %arrayidx7, align 1
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br label %for.inc
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for.inc: ; preds = %if.end
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%7 = load i32, i32* @e, align 4
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%inc = add nsw i32 %7, 1
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store i32 %inc, i32* @e, align 4
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br label %for.cond3
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for.end: ; preds = %for.cond3
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br label %for.inc8
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for.inc8: ; preds = %for.end
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%8 = load i32, i32* @d, align 4
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%inc9 = add nsw i32 %8, 1
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store i32 %inc9, i32* @d, align 4
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br label %for.cond
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for.end10: ; preds = %for.cond
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ret void
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}
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; Function Attrs: nounwind uwtable
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define i32 @main() {
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entry:
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%retval = alloca i32, align 4
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store i32 0, i32* %retval
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call void @fn1()
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%0 = load i8, i8* getelementptr inbounds ([1 x [3 x i8]], [1 x [3 x i8]]* @f, i32 0, i64 0, i64 1), align 1
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%conv = sext i8 %0 to i32
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%cmp = icmp ne i32 %conv, 1
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br i1 %cmp, label %if.then, label %if.end
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if.then: ; preds = %entry
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call void @abort()
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unreachable
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if.end: ; preds = %entry
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ret i32 0
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}
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; Function Attrs: noreturn nounwind
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declare void @abort()
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