[ValueTracking, InstCombine] extend isKnownToBeAPowerOfTwo() to handle vector splat constants

We could try harder to handle non-splat vector constants too, 
but that seems much rarer to me.

Note that the div test isn't resolved because there's a check
for isIntegerTy() guarding that transform.

Differential Revision: http://reviews.llvm.org/D20497

llvm-svn: 270369

4 files changed, 8 insertions, 13 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 19fef59e1f3..38853478c06 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1500,9 +1500,10 @@ bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth,
   if (Constant *C = dyn_cast<Constant>(V)) {
     if (C->isNullValue())
       return OrZero;
-    if (ConstantInt *CI = dyn_cast<ConstantInt>(C))
-      return CI->getValue().isPowerOf2();
-    // TODO: Handle vector constants.
+
+    const APInt *ConstIntOrConstSplatInt;
+    if (match(C, m_APInt(ConstIntOrConstSplatInt)))
+      return ConstIntOrConstSplatInt->isPowerOf2();
   }
 
   // 1 << X is clearly a power of two if the one is not shifted off the end.  If
diff --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
index e4fd3324777..2b7c907f177 100644
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -374,7 +374,7 @@ define i32 @test36(i32 %A) {
 define <2 x i32> @test36vec(<2 x i32> %A) {
 ; CHECK-LABEL: @test36vec(
 ; CHECK-NEXT:    [[AND:%.*]] = and <2 x i32> %A, <i32 2147483647, i32 2147483647>
-; CHECK-NEXT:    [[SHL:%.*]] = shl nsw <2 x i32> <i32 1, i32 1>, %A
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw nsw <2 x i32> <i32 1, i32 1>, %A
 ; CHECK-NEXT:    [[MUL:%.*]] = sdiv exact <2 x i32> [[AND]], [[SHL]]
 ; CHECK-NEXT:    ret <2 x i32> [[MUL]]
 ;
diff --git a/llvm/test/Transforms/InstCombine/rem.ll b/llvm/test/Transforms/InstCombine/rem.ll
index 9f65228dee1..227344f16f2 100644
--- a/llvm/test/Transforms/InstCombine/rem.ll
+++ b/llvm/test/Transforms/InstCombine/rem.ll
@@ -25,22 +25,18 @@ define i32 @test3(i32 %A) {
 	ret i32 %B
 }
 
-; FIXME: This could be an 'and' just like above.
-
 define <2 x i32> @vec_power_of_2_constant_splat_divisor(<2 x i32> %A) {
 ; CHECK-LABEL: @vec_power_of_2_constant_splat_divisor(
-; CHECK-NEXT:    [[B:%.*]] = urem <2 x i32> %A, <i32 8, i32 8>
+; CHECK-NEXT:    [[B:%.*]] = and <2 x i32> %A, <i32 7, i32 7>
 ; CHECK-NEXT:    ret <2 x i32> [[B]]
 ;
   %B = urem <2 x i32> %A, <i32 8, i32 8>
   ret <2 x i32> %B
 }
 
-; FIXME: And it shouldn't matter whether we have ConstantVector or ConstantDataVector.
-
 define <2 x i19> @weird_vec_power_of_2_constant_splat_divisor(<2 x i19> %A) {
 ; CHECK-LABEL: @weird_vec_power_of_2_constant_splat_divisor(
-; CHECK-NEXT:    [[B:%.*]] = urem <2 x i19> %A, <i19 8, i19 8>
+; CHECK-NEXT:    [[B:%.*]] = and <2 x i19> %A, <i19 7, i19 7>
 ; CHECK-NEXT:    ret <2 x i19> [[B]]
 ;
   %B = urem <2 x i19> %A, <i19 8, i19 8>
diff --git a/llvm/test/Transforms/InstCombine/shift.ll b/llvm/test/Transforms/InstCombine/shift.ll
index e4dd377952a..755c4a7f9f1 100644
--- a/llvm/test/Transforms/InstCombine/shift.ll
+++ b/llvm/test/Transforms/InstCombine/shift.ll
@@ -700,11 +700,9 @@ define i32 @test42(i32 %a, i32 %b) nounwind {
   ret i32 %div2
 }
 
-; FIXME: Vector lshr should be treated the same as scalar. 
-
 define <2 x i32> @test42vec(<2 x i32> %a, <2 x i32> %b) {
 ; CHECK-LABEL: @test42vec(
-; CHECK-NEXT:    [[DIV:%.*]] = lshr <2 x i32> <i32 4096, i32 4096>, %b
+; CHECK-NEXT:    [[DIV:%.*]] = lshr exact <2 x i32> <i32 4096, i32 4096>, %b
 ; CHECK-NEXT:    [[DIV2:%.*]] = udiv <2 x i32> %a, [[DIV]]
 ; CHECK-NEXT:    ret <2 x i32> [[DIV2]]
 ;