[PATCH] D48828: [InstSimplify] fold extracting from std::pair (1/2)

[Hiroshi Inoue via Phabricator via llvm-commits]

inouehrs updated this revision to Diff 158182.

https://reviews.llvm.org/D48828

Files:
  lib/Analysis/InstructionSimplify.cpp
  test/Transforms/InstSimplify/shift.ll


Index: test/Transforms/InstSimplify/shift.ll
===================================================================
--- test/Transforms/InstSimplify/shift.ll
+++ test/Transforms/InstSimplify/shift.ll
@@ -178,11 +178,7 @@
 define i64 @shl_or_shr(i32 %a, i32 %b) {
 ; CHECK-LABEL: @shl_or_shr(
 ; CHECK-NEXT:    [[TMP1:%.*]] = zext i32 [[A:%.*]] to i64
-; CHECK-NEXT:    [[TMP2:%.*]] = zext i32 [[B:%.*]] to i64
-; CHECK-NEXT:    [[TMP3:%.*]] = shl nuw i64 [[TMP1]], 32
-; CHECK-NEXT:    [[TMP4:%.*]] = or i64 [[TMP2]], [[TMP3]]
-; CHECK-NEXT:    [[TMP5:%.*]] = lshr i64 [[TMP4]], 32
-; CHECK-NEXT:    ret i64 [[TMP5]]
+; CHECK-NEXT:    ret i64 [[TMP1]]
 ;
   %tmp1 = zext i32 %a to i64
   %tmp2 = zext i32 %b to i64
@@ -214,11 +210,7 @@
 define <2 x i64> @shl_or_shr1v(<2 x i32> %a, <2 x i32> %b) {
 ; CHECK-LABEL: @shl_or_shr1v(
 ; CHECK-NEXT:    [[TMP1:%.*]] = zext <2 x i32> [[A:%.*]] to <2 x i64>
-; CHECK-NEXT:    [[TMP2:%.*]] = zext <2 x i32> [[B:%.*]] to <2 x i64>
-; CHECK-NEXT:    [[TMP3:%.*]] = shl nuw <2 x i64> [[TMP1]], <i64 32, i64 32>
-; CHECK-NEXT:    [[TMP4:%.*]] = or <2 x i64> [[TMP3]], [[TMP2]]
-; CHECK-NEXT:    [[TMP5:%.*]] = lshr <2 x i64> [[TMP4]], <i64 32, i64 32>
-; CHECK-NEXT:    ret <2 x i64> [[TMP5]]
+; CHECK-NEXT:    ret <2 x i64> [[TMP1]]
 ;
   %tmp1 = zext <2 x i32> %a to <2 x i64>
   %tmp2 = zext <2 x i32> %b to <2 x i64>
Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -1317,6 +1317,23 @@
   if (match(Op0, m_NUWShl(m_Value(X), m_Specific(Op1))))
     return X;
 
+  // ((X << A) | Y) >> A -> X  if effective width of Y is not larger than A.
+  // We can return X as we do in the above case since OR alters no bits in X.
+  // SimplifyDemandedBits in InstCombine can do more general optimization for
+  // bit manipulation. This pattern aims to provide opportunities for other
+  // optimizers by supporting a simple but common case in InstSimplify.
+  Value *Y;
+  const APInt *ShRAmt, *ShLAmt;
+  if (match(Op1, m_APInt(ShRAmt)) &&
+      match(Op0, m_c_Or(m_NUWShl(m_Value(X), m_APInt(ShLAmt)), m_Value(Y))) &&
+      *ShRAmt == *ShLAmt) {
+    const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
+    const unsigned Width = Op0->getType()->getScalarSizeInBits();
+    const unsigned EffWidthY = Width - YKnown.countMinLeadingZeros();
+    if (EffWidthY <= ShRAmt->getZExtValue())
+      return X;
+  }
+
   return nullptr;
 }
 


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