4698bf145d
This reverts commit41784bed01. Since the original revisionead815924e, 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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