Revert "Revert "This patch builds on top of D13378 to handle constant condition.""

This reverts commit r249528 and reapply r249431. The fix for the
fallout has been commited in r249575.

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 249581

2 files changed, 56 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 6386082ca91..3a4de1aec6d 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/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/llvm/test/Analysis/ScalarEvolution/constant_condition.ll b/llvm/test/Analysis/ScalarEvolution/constant_condition.ll
new file mode 100644
index 00000000000..32ab91b2c85
--- /dev/null
+++ b/llvm/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
+}