[llvm-dev] [cfe-dev] [RFC] Loading Bitfields with Smallest Needed Types (original) (raw)

Carrot Wei via llvm-dev llvm-dev at lists.llvm.org
Wed May 27 10:04:32 PDT 2020

Similar issue with aligned extload widening. The load and store are both i16 in IR.

struct s { int x; // force alignment short y; };

void g(); short f2(s *a, short b) { a->y = b; g(); return a->y - b; }

produces this movq %rdi, %rbx movw %bp, 4(%rdi) // 2 byte store callq g() movl 4(%rbx), %eax // 4 byte load subl %ebp, %eax

~Craig

It is caused by loadi32:

def loadi32 : PatFrag<(ops node:$ptr), (i32 (unindexedload node:$ptr)), [{ LoadSDNode *LD = cast(N); ISD::LoadExtType ExtType = LD->getExtensionType(); if (ExtType == ISD::NON_EXTLOAD) return true; if (ExtType == ISD::EXTLOAD) // * return LD->getAlignment() >= 4 && LD->isSimple(); // * return false; }]>;

Without the commented lines, movzwl should be generated. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200527/28813681/attachment.html>

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