From e79f96c7c6aa2fb1117757581a6f96cac636a58e Mon Sep 17 00:00:00 2001
From: Mehdi Amini <mehdi.amini@apple.com>
Date: Tue, 6 Oct 2015 17:19:20 +0000
Subject: [PATCH] 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@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249431 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp              |  5 ++
 .../ScalarEvolution/constant_condition.ll     | 51 +++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 test/Analysis/ScalarEvolution/constant_condition.ll

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 9715d83fd10..caa0899f6a9 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -3904,6 +3904,11 @@ const SCEV *ScalarEvolution::createNodeForSelectOrPHI(Instruction *I,
                                                       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)
diff --git a/test/Analysis/ScalarEvolution/constant_condition.ll b/test/Analysis/ScalarEvolution/constant_condition.ll
new file mode 100644
index 00000000000..32ab91b2c85
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/constant_condition.ll
@@ -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
+}
-- 
2.34.1