[InstCombine] In foldSelectICmpAnd, if we need to to truncate from the 'and' type...

Previously we were always trying to emit the zext or truncate before any shift. This meant if the 'and' mask was larger than the size of the truncate we would skip the transformation.

Now we shift the result of the and right first leaving the bit within the range of the truncate.

This matches what we are doing in foldSelectICmpAndOr for the same problem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310159 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 9ef6a0e..b5b8aa3 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -640,16 +640,16 @@ static Value *foldSelectICmpAnd(const SelectInst &SI, const ICmpInst *IC,
   unsigned AndZeros = AndRHS->getValue().logBase2();
 
   // If types don't match we can still convert the select by introducing a zext
-  // or a trunc of the 'and'. The trunc case requires that all of the truncated
-  // bits are zero, we can figure that out by looking at the 'and' mask.
-  if (AndZeros >= ValC.getBitWidth())
-    return nullptr;
-
-  Value *V = Builder.CreateZExtOrTrunc(LHS, SI.getType());
-  if (ValZeros > AndZeros)
+  // or a trunc of the 'and'.
+  Value *V = LHS;
+  if (ValZeros > AndZeros) {
+    V = Builder.CreateZExtOrTrunc(V, SI.getType());
     V = Builder.CreateShl(V, ValZeros - AndZeros);
-  else if (ValZeros < AndZeros)
+  } else if (ValZeros < AndZeros) {
     V = Builder.CreateLShr(V, AndZeros - ValZeros);
+    V = Builder.CreateZExtOrTrunc(V, SI.getType());
+  } else
+    V = Builder.CreateZExtOrTrunc(V, SI.getType());
 
   // Okay, now we know that everything is set up, we just don't know whether we
   // have a icmp_ne or icmp_eq and whether the true or false val is the zero.

diff --git a/test/Transforms/InstCombine/select-with-bitwise-ops.ll b/test/Transforms/InstCombine/select-with-bitwise-ops.ll
index f562c6e..c92a749 100644 (file)
--- a/test/Transforms/InstCombine/select-with-bitwise-ops.ll
+++ b/test/Transforms/InstCombine/select-with-bitwise-ops.ll
@@ -256,11 +256,11 @@ define i32 @select_icmp_x_and_2147483648_ne_0_or_2147483648(i32 %x) {
 
 define i32 @test65(i64 %x) {
 ; CHECK-LABEL: @test65(
-; CHECK-NEXT:    [[X_TR:%.*]] = trunc i64 %x to i32
-; CHECK-NEXT:    [[TMP1:%.*]] = lshr i32 [[X_TR]], 3
-; CHECK-NEXT:    [[TMP2:%.*]] = and i32 [[TMP1]], 2
-; CHECK-NEXT:    [[TMP3:%.*]] = xor i32 [[TMP2]], 42
-; CHECK-NEXT:    ret i32 [[TMP3]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i64 [[X:%.*]], 3
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[TMP1]] to i32
+; CHECK-NEXT:    [[TMP3:%.*]] = and i32 [[TMP2]], 2
+; CHECK-NEXT:    [[TMP4:%.*]] = xor i32 [[TMP3]], 42
+; CHECK-NEXT:    ret i32 [[TMP4]]
 ;
   %1 = and i64 %x, 16
   %2 = icmp ne i64 %1, 0
@@ -270,10 +270,11 @@ define i32 @test65(i64 %x) {
 
 define i32 @test66(i64 %x) {
 ; CHECK-LABEL: @test66(
-; CHECK-NEXT:    [[TMP1:%.*]] = and i64 %x, 4294967296
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[TMP1]], 0
-; CHECK-NEXT:    [[TMP3:%.*]] = select i1 [[TMP2]], i32 42, i32 40
-; CHECK-NEXT:    ret i32 [[TMP3]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i64 [[X:%.*]], 31
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[TMP1]] to i32
+; CHECK-NEXT:    [[TMP3:%.*]] = and i32 [[TMP2]], 2
+; CHECK-NEXT:    [[TMP4:%.*]] = xor i32 [[TMP3]], 42
+; CHECK-NEXT:    ret i32 [[TMP4]]
 ;
   %1 = and i64 %x, 4294967296
   %2 = icmp ne i64 %1, 0