Teach ValueTracking a new way to analyze PHI nodes, and and teach

Instcombine to be more aggressive about using SimplifyDemandedBits
on shift nodes. This allows a shift to be simplified to zero in the
included test case.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72204 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 35 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/lshr-phi.ll b/test/Transforms/InstCombine/lshr-phi.ll
new file mode 100644
index 0000000000..683eb87931
--- /dev/null
+++ b/test/Transforms/InstCombine/lshr-phi.ll
@@ -0,0 +1,35 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis > %t
+; RUN: not grep lshr %t
+; RUN: grep add %t | count 1
+
+; Instcombine should be able to eliminate the lshr, because only
+; bits in the operand which might be non-zero will be shifted
+; off the end.
+
+define i32 @hash_string(i8* nocapture %key) nounwind readonly {
+entry:
+	%t0 = load i8* %key, align 1		; <i8> [#uses=1]
+	%t1 = icmp eq i8 %t0, 0		; <i1> [#uses=1]
+	br i1 %t1, label %bb2, label %bb
+
+bb:		; preds = %bb, %entry
+	%indvar = phi i64 [ 0, %entry ], [ %tmp, %bb ]		; <i64> [#uses=2]
+	%k.04 = phi i32 [ 0, %entry ], [ %t8, %bb ]		; <i32> [#uses=2]
+	%cp.05 = getelementptr i8* %key, i64 %indvar		; <i8*> [#uses=1]
+	%t2 = shl i32 %k.04, 1		; <i32> [#uses=1]
+	%t3 = lshr i32 %k.04, 14		; <i32> [#uses=1]
+	%t4 = add i32 %t2, %t3		; <i32> [#uses=1]
+	%t5 = load i8* %cp.05, align 1		; <i8> [#uses=1]
+	%t6 = sext i8 %t5 to i32		; <i32> [#uses=1]
+	%t7 = xor i32 %t6, %t4		; <i32> [#uses=1]
+	%t8 = and i32 %t7, 16383		; <i32> [#uses=2]
+	%tmp = add i64 %indvar, 1		; <i64> [#uses=2]
+	%scevgep = getelementptr i8* %key, i64 %tmp		; <i8*> [#uses=1]
+	%t9 = load i8* %scevgep, align 1		; <i8> [#uses=1]
+	%t10 = icmp eq i8 %t9, 0		; <i1> [#uses=1]
+	br i1 %t10, label %bb2, label %bb
+
+bb2:		; preds = %bb, %entry
+	%k.0.lcssa = phi i32 [ 0, %entry ], [ %t8, %bb ]		; <i32> [#uses=1]
+	ret i32 %k.0.lcssa
+}