[PATCH] D32240: InstCombineCast AShr transformation

[David Majnemer via Phabricator via llvm-commits]

majnemer added a comment.

This needs a testcase.



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Comment at: InstCombineCasts.cpp:1258-1262
+  //   %shr26 = lshr i32 %0, 16                        ; [#uses=1 type=i32]
+  //   %conv4 = trunc i32 %shr26 to i16                ; [#uses=1 type=i16]
+  //   %3 = sext i16 %conv4 to i32                     ; [#uses=N type=i32]
+  // To:
+  //   %3 = ashr i32 %0, 16
----------------
Please use more regular register names and elide the commends.


================
Comment at: InstCombineCasts.cpp:1263
+  //   %3 = ashr i32 %0, 16
+  if (match(Src, m_OneUse(m_Trunc( m_OneUse(m_LShr(m_Value(A), m_ConstantInt(BA)))))) &&
+      A->getType() == CI.getType()) {
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I'd recommend using m_APInt so that it will match against vectors.


================
Comment at: InstCombineCasts.cpp:1267
+    unsigned TruncSize = Src->getType()->getScalarSizeInBits();
+    if (BA->getZExtValue() == SextSize - TruncSize)
+      return BinaryOperator::CreateAShr(A, BA);
----------------
This will explode if the ConstantInt is bigger than an i64


Repository:
  rL LLVM

https://reviews.llvm.org/D32240