When turning (ashr(shl(x, n), n)) into sext(trunc(x)), the width of the

type to truncate to should be the number of bits of the value that are
preserved, not the number that are clobbered with sign-extension.
This fixes regressions in ldecod.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@69704 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 30 insertions, 1 deletions

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index ace063a399..0aa673f355 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2015,7 +2015,7 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
       if (Instruction *L = dyn_cast<Instruction>(U->getOperand(0)))
         if (L->getOpcode() == Instruction::Shl &&
             L->getOperand(1) == U->getOperand(1)) {
-          uint64_t Amt = CI->getZExtValue();
+          uint64_t Amt = getTypeSizeInBits(U->getType()) - CI->getZExtValue();
           return
             SE.getSignExtendExpr(SE.getTruncateExpr(getSCEV(L->getOperand(0)),
                                                     IntegerType::get(Amt)),
diff --git a/test/Analysis/ScalarEvolution/sext-inreg.ll b/test/Analysis/ScalarEvolution/sext-inreg.ll
new file mode 100644
index 0000000000..c482fe6cf5
--- /dev/null
+++ b/test/Analysis/ScalarEvolution/sext-inreg.ll
@@ -0,0 +1,29 @@
+; RUN: llvm-as < %s | opt -analyze -scalar-evolution -disable-output \
+; RUN:  | grep {signextend \{0,+,199\}<bb> to i64} | count 2
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
+target triple = "i386-apple-darwin9.6"
+
+define i64 @foo(i64* nocapture %x, i64 %n) nounwind {
+entry:
+	%t0 = icmp sgt i64 %n, 0		; <i1> [#uses=1]
+	br i1 %t0, label %bb, label %return
+
+bb:		; preds = %bb, %entry
+	%i.01 = phi i64 [ 0, %entry ], [ %indvar.next, %bb ]		; <i32> [#uses=2]
+	%t1 = shl i64 %i.01, 7		; <i32> [#uses=1]
+	%t2 = ashr i64 %t1, 7		; <i32> [#uses=1]
+	%s1 = shl i64 %i.01, 5		; <i32> [#uses=1]
+	%s2 = ashr i64 %s1, 5		; <i32> [#uses=1]
+	%t3 = getelementptr i64* %x, i64 %i.01		; <i64*> [#uses=1]
+	store i64 0, i64* %t3, align 1
+	%indvar.next = add i64 %i.01, 199		; <i32> [#uses=2]
+	%exitcond = icmp eq i64 %indvar.next, %n		; <i1> [#uses=1]
+	br i1 %exitcond, label %return, label %bb
+
+return:		; preds = %bb, %entry
+        %p = phi i64 [ 0, %entry ], [ %t2, %bb ]
+        %q = phi i64 [ 0, %entry ], [ %s2, %bb ]
+        %v = xor i64 %p, %q
+	ret i64 %v
+}