[SCEV] Don't create SCEV expressions that break LCSSA

Prevent `createNodeFromSelectLikePHI` from creating SCEV expressions
that break LCSSA.

A better fix for the same issue is to teach SCEVExpander to not break
LCSSA by inserting PHI nodes at appropriate places.  That's planned for
the future.

Fixes PR25360.

llvm-svn: 251756

2 files changed, 57 insertions, 0 deletions

diff --git a/llvm/test/Analysis/ScalarEvolution/smax-br-phi-idioms.ll b/llvm/test/Analysis/ScalarEvolution/smax-br-phi-idioms.ll
index 2657982979d..500f3e16c8f 100644
--- a/llvm/test/Analysis/ScalarEvolution/smax-br-phi-idioms.ll
+++ b/llvm/test/Analysis/ScalarEvolution/smax-br-phi-idioms.ll
@@ -102,3 +102,27 @@ define i32 @f4(i32 %x, i32 %init, i32 %lim) {
 ; CHECK-NEXT:  -->  %v U: full-set S: full-set
   ret i32 %v
 }
+
+define i32 @f5(i32* %val) {
+; CHECK-LABEL: Classifying expressions for: @f5
+entry:
+  br label %for.end
+
+for.condt:
+  br i1 true, label %for.cond.0, label %for.end
+
+for.end:
+  %inc = load i32, i32* %val
+  br i1 false, label %for.condt, label %for.cond.0
+
+for.cond.0:
+  %init = phi i32 [ 0, %for.condt ], [ %inc, %for.end ]
+
+; CHECK:  %init = phi i32 [ 0, %for.condt ], [ %inc, %for.end ]
+; CHECK-NEXT:  -->  %init U: full-set S: full-set
+
+; Matching "through" %init will break LCSSA at the SCEV expression
+; level.
+
+  ret i32 %init
+}
diff --git a/llvm/test/Transforms/IndVarSimplify/pr25360.ll b/llvm/test/Transforms/IndVarSimplify/pr25360.ll
new file mode 100644
index 00000000000..9f6df7051ea
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/pr25360.ll
@@ -0,0 +1,33 @@
+; RUN: opt -indvars -S < %s | FileCheck %s
+
+
+; Ensure that does not crash
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @f() {
+; CHECK-LABEL: @f(
+entry:
+  br label %for.end
+
+for.condt:                         ; preds = %for.end
+  br i1 true, label %for.cond.0, label %for.end
+
+for.end:                                          ; preds = %for.body.3
+  %inc = select i1 undef, i32 2, i32 1
+  br i1 false, label %for.condt, label %for.cond.0
+
+for.cond.0:                       ; preds = %for.end, %for.condt
+  %init = phi i32 [ 0, %for.condt ], [ %inc, %for.end ]
+  br i1 true, label %for.end.13, label %for.body.9
+
+for.body.9:                                       ; preds = %for.body.9, %for.cond.0
+  %p1.addr.22 = phi i32 [ %inc10, %for.body.9 ], [ %init, %for.cond.0 ]
+  %inc10 = add i32 %p1.addr.22, 1
+  br i1 true, label %for.end.13, label %for.body.9
+
+for.end.13:                                       ; preds = %for.cond.7.for.end.13_crit_edge, %for.cond.0
+  %p1.addr.2.lcssa = phi i32 [ %inc10, %for.body.9 ], [ %init, %for.cond.0 ]
+  ret void
+}