4698bf145d
This reverts commit 41784bed01543315a1d03141e6ddc023fd914c0b.
Since the original revision ead815924e6ebeaf02c31c37ebf7a560b5fdf67b,
this revision fixes three issues:
- This revision fixes the Windows build. My original patch improperly
copied EH pads on Windows. This patch disregards jump threading
opportunities having to do with EH pads.
- This revision fixes jump threading to a wrong destination.
Specifically, my original patch treated any Constant other than 0 as 1
while evaluating the branch condition. This bug led to treating
constant expressions like:
icmp ugt i8* null, inttoptr (i64 4 to i8*)
to "true". This patch fixes the bug by calling isOneValue.
- This revision fixes the cost calculation of two basic blocks being
threaded through. Note that getJumpThreadDuplicationCost returns
"(unsigned)~0" for those basic blocks that cannot be duplicated. If
we sum of two return values from getJumpThreadDuplicationCost, we
could have an unsigned overflow like:
(unsigned)~0 + 5 = 4
and mistakenly determine that it's safe and profitable to proceed
with the jump threading opportunity. The patch fixes the bug by
checking each return value before summing them up.
[JumpThreading] Thread jumps through two basic blocks
Summary:
This patch teaches JumpThreading.cpp to thread through two basic
blocks like:
bb3:
%var = phi i32* [ null, %bb1 ], [ @a, %bb2 ]
%tobool = icmp eq i32 %cond, 0
br i1 %tobool, label %bb4, label ...
bb4:
%cmp = icmp eq i32* %var, null
br i1 %cmp, label bb5, label bb6
by duplicating basic blocks like bb3 above. Once we duplicate bb3 as
bb3.dup and redirect edge bb2->bb3 to bb2->bb3.dup, we have:
bb3:
%var = phi i32* [ @a, %bb2 ]
%tobool = icmp eq i32 %cond, 0
br i1 %tobool, label %bb4, label ...
bb3.dup:
%var = phi i32* [ null, %bb1 ]
%tobool = icmp eq i32 %cond, 0
br i1 %tobool, label %bb4, label ...
bb4:
%cmp = icmp eq i32* %var, null
br i1 %cmp, label bb5, label bb6
Then the existing code in JumpThreading.cpp can thread edge
bb3.dup->bb4 through bb4 and eventually create bb3.dup->bb5.
Reviewers: wmi
Subscribers: hiraditya, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70247
57 lines
1.3 KiB
LLVM
57 lines
1.3 KiB
LLVM
; RUN: opt < %s -jump-threading -S -verify | FileCheck %s
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target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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define void @foo(i32 %cond1, i32 %cond2) {
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; CHECK-LABEL: @foo
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; CHECK-LABEL: entry
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entry:
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%tobool = icmp ne i32 %cond1, 0
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br i1 %tobool, label %bb.f1, label %bb.f2
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bb.f1:
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call void @f1()
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br label %bb.cond2
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; Verify that we branch on cond2 without checking tobool again.
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; CHECK: call void @f1()
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; CHECK-NEXT: icmp eq i32 %cond2, 0
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; CHECK-NEXT: label %exit, label %bb.f3
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bb.f2:
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call void @f2()
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br label %bb.cond2
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; Verify that we branch on cond2 without checking tobool again.
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; CHECK: call void @f2()
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; CHECK-NEXT: icmp eq i32 %cond2, 0
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; CHECK-NEXT: label %exit, label %bb.f4
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bb.cond2:
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%tobool1 = icmp eq i32 %cond2, 0
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br i1 %tobool1, label %exit, label %bb.cond1again
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; Verify that we eliminate this basic block.
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; CHECK-NOT: bb.cond1again:
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bb.cond1again:
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br i1 %tobool, label %bb.f3, label %bb.f4
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bb.f3:
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call void @f3()
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br label %exit
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bb.f4:
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call void @f4()
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br label %exit
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exit:
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ret void
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}
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declare void @f1() local_unnamed_addr
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declare void @f2() local_unnamed_addr
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declare void @f3() local_unnamed_addr
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declare void @f4() local_unnamed_addr
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