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| author | Stephen Hines <srhines@google.com> | 2014-04-23 16:57:46 -0700 |
|---|---|---|
| committer | Stephen Hines <srhines@google.com> | 2014-04-24 15:53:16 -0700 |
| commit | 36b56886974eae4f9c5ebc96befd3e7bfe5de338 (patch) | |
| tree | e6cfb69fbbd937f450eeb83bfb83b9da3b01275a /lib/Target/X86/README.txt | |
| parent | 69a8640022b04415ae9fac62f8ab090601d8f889 (diff) | |
| download | external_llvm-36b56886974eae4f9c5ebc96befd3e7bfe5de338.zip external_llvm-36b56886974eae4f9c5ebc96befd3e7bfe5de338.tar.gz external_llvm-36b56886974eae4f9c5ebc96befd3e7bfe5de338.tar.bz2 | |
Update to LLVM 3.5a.
Change-Id: Ifadecab779f128e62e430c2b4f6ddd84953ed617
Diffstat (limited to 'lib/Target/X86/README.txt')
| -rw-r--r-- | lib/Target/X86/README.txt | 50 |
1 files changed, 1 insertions, 49 deletions
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt index b4285a0..52d3c01 100644 --- a/lib/Target/X86/README.txt +++ b/lib/Target/X86/README.txt @@ -123,7 +123,7 @@ flags. The instruction selector sometimes misses folding a load into a compare. The pattern is written as (cmp reg, (load p)). Because the compare isn't commutative, it is not matched with the load on both sides. The dag combiner -should be made smart enough to cannonicalize the load into the RHS of a compare +should be made smart enough to canonicalize the load into the RHS of a compare when it can invert the result of the compare for free. //===---------------------------------------------------------------------===// @@ -1444,54 +1444,6 @@ it would be nice to produce "into" someday. //===---------------------------------------------------------------------===// -This code: - -void vec_mpys1(int y[], const int x[], int scaler) { -int i; -for (i = 0; i < 150; i++) - y[i] += (((long long)scaler * (long long)x[i]) >> 31); -} - -Compiles to this loop with GCC 3.x: - -.L5: - movl %ebx, %eax - imull (%edi,%ecx,4) - shrdl $31, %edx, %eax - addl %eax, (%esi,%ecx,4) - incl %ecx - cmpl $149, %ecx - jle .L5 - -llvm-gcc compiles it to the much uglier: - -LBB1_1: ## bb1 - movl 24(%esp), %eax - movl (%eax,%edi,4), %ebx - movl %ebx, %ebp - imull %esi, %ebp - movl %ebx, %eax - mull %ecx - addl %ebp, %edx - sarl $31, %ebx - imull %ecx, %ebx - addl %edx, %ebx - shldl $1, %eax, %ebx - movl 20(%esp), %eax - addl %ebx, (%eax,%edi,4) - incl %edi - cmpl $150, %edi - jne LBB1_1 ## bb1 - -The issue is that we hoist the cast of "scaler" to long long outside of the -loop, the value comes into the loop as two values, and -RegsForValue::getCopyFromRegs doesn't know how to put an AssertSext on the -constructed BUILD_PAIR which represents the cast value. - -This can be handled by making CodeGenPrepare sink the cast. - -//===---------------------------------------------------------------------===// - Test instructions can be eliminated by using EFLAGS values from arithmetic instructions. This is currently not done for mul, and, or, xor, neg, shl, sra, srl, shld, shrd, atomic ops, and others. It is also currently not done |