[llvm] r249431 - This patch builds on top of D13378 to handle constant condition.

[Sanjoy Das via llvm-commits]

I'm pretty sure that the crash is fixed by this: http://reviews.llvm.org/D13461 -- indvars RAUW'ed a LCSSA phi with a 
use outside the loop.

Mehdi Amini via llvm-commits wrote:
>
>> On Oct 7, 2015, at 2:06 AM, James Molloy <james at jamesmolloy.co.uk <mailto:james at jamesmolloy.co.uk>> wrote:
>>
>> Hi Mehdi,
>>
>> I've reverted this in r249528 as it was causing failures in all our internal builders and here too:
>> http://lab.llvm.org:8011/builders/clang-native-arm-lnt/builds/14453
>>
>> Apologies,
>
> No need to apologize, thanks for reverting, I’ll try to repro and figure out what went wrong.
>
> —
> Mehdi
>
>
>
>>
>> James
>>
>> On Tue, 6 Oct 2015 at 18:21 Mehdi Amini via llvm-commits <llvm-commits at lists.llvm.org
>> <mailto:llvm-commits at lists.llvm.org>> wrote:
>>
>>     Author: mehdi_amini
>>     Date: Tue Oct 6 12:19:20 2015
>>     New Revision: 249431
>>
>>     URL: http://llvm.org/viewvc/llvm-project?rev=249431&view=rev <http://llvm.org/viewvc/llvm-project?rev=249431&view=rev>
>>     Log:
>>     This patch builds on top of D13378 to handle constant condition.
>>
>>     With this patch, clang -O3 optimizes correctly providing > 1000x speedup on this artificial benchmark):
>>
>>     for (a=0; a<n; a++)
>>     for (b=0; b<n; b++)
>>     for (c=0; c<n; c++)
>>     for (d=0; d<n; d++)
>>     for (e=0; e<n; e++)
>>     for (f=0; f<n; f++)
>>     x++;
>>     From test-suite/SingleSource/Benchmarks/Shootout/nestedloop.c
>>
>>     Reviewers: sanjoyd
>>
>>     Differential Revision: http://reviews.llvm.org/D13390
>>
>>     From: Mehdi Amini <mehdi.amini at apple.com <mailto:mehdi.amini at apple.com>>
>>
>>     Added:
>>     llvm/trunk/test/Analysis/ScalarEvolution/constant_condition.ll
>>     Modified:
>>     llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>>
>>     Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
>>     URL:
>>     http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=249431&r1=249430&r2=249431&view=diff
>>     <http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=249431&r1=249430&r2=249431&view=diff>
>>     ==============================================================================
>>     --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
>>     +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Tue Oct 6 12:19:20 2015
>>     @@ -3904,6 +3904,11 @@ const SCEV *ScalarEvolution::createNodeF
>>     Value *Cond,
>>     Value *TrueVal,
>>     Value *FalseVal) {
>>     + // Handle "constant" branch or select. This can occur for instance when a
>>     + // loop pass transforms an inner loop and moves on to process the outer loop.
>>     + if (auto *CI = dyn_cast<ConstantInt>(Cond))
>>     + return getSCEV(CI->isOne() ? TrueVal : FalseVal);
>>     +
>>     // Try to match some simple smax or umax patterns.
>>     auto *ICI = dyn_cast<ICmpInst>(Cond);
>>     if (!ICI)
>>
>>     Added: llvm/trunk/test/Analysis/ScalarEvolution/constant_condition.ll
>>     URL:
>>     http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/constant_condition.ll?rev=249431&view=auto
>>     <http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/constant_condition.ll?rev=249431&view=auto>
>>     ==============================================================================
>>     --- llvm/trunk/test/Analysis/ScalarEvolution/constant_condition.ll (added)
>>     +++ llvm/trunk/test/Analysis/ScalarEvolution/constant_condition.ll Tue Oct 6 12:19:20 2015
>>     @@ -0,0 +1,51 @@
>>     +; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
>>     +
>>     +define i32 @branch_true(i32 %x, i32 %y) {
>>     +; CHECK-LABEL: Classifying expressions for: @branch_true
>>     + entry:
>>     + br i1 true, label %add, label %merge
>>     +
>>     + add:
>>     + %sum = add i32 %x, %y
>>     + br label %merge
>>     +
>>     + merge:
>>     + %v = phi i32 [ %sum, %add ], [ %x, %entry ]
>>     +; CHECK: %v = phi i32 [ %sum, %add ], [ %x, %entry ]
>>     +; CHECK-NEXT: --> (%x + %y) U: full-set S: full-set
>>     + ret i32 %v
>>     +}
>>     +
>>     +define i32 @branch_false(i32 %x, i32 %y) {
>>     +; CHECK-LABEL: Classifying expressions for: @branch_false
>>     + entry:
>>     + br i1 false, label %add, label %merge
>>     +
>>     + add:
>>     + %sum = add i32 %x, %y
>>     + br label %merge
>>     +
>>     + merge:
>>     + %v = phi i32 [ %sum, %add ], [ %x, %entry ]
>>     +; CHECK: %v = phi i32 [ %sum, %add ], [ %x, %entry ]
>>     +; CHECK-NEXT: --> %x U: full-set S: full-set
>>     + ret i32 %v
>>     +}
>>     +
>>     +define i32 @select_true(i32 %x, i32 %y) {
>>     +; CHECK-LABEL: Classifying expressions for: @select_true
>>     + entry:
>>     + %v = select i1 true, i32 %x, i32 %y
>>     +; CHECK: %v = select i1 true, i32 %x, i32 %y
>>     +; CHECK-NEXT: --> %x U: full-set S: full-set
>>     + ret i32 %v
>>     +}
>>     +
>>     +define i32 @select_false(i32 %x, i32 %y) {
>>     +; CHECK-LABEL: Classifying expressions for: @select_false
>>     + entry:
>>     + %v = select i1 false, i32 %x, i32 %y
>>     +; CHECK: %v = select i1 false, i32 %x, i32 %y
>>     +; CHECK-NEXT: --> %y U: full-set S: full-set
>>     + ret i32 %v
>>     +}
>>
>>
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