diff options
Diffstat (limited to 'lib/Target/X86/README.txt')
| -rw-r--r-- | lib/Target/X86/README.txt | 44 |
1 files changed, 0 insertions, 44 deletions
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt index 1588b49e6f..ceda932001 100644 --- a/lib/Target/X86/README.txt +++ b/lib/Target/X86/README.txt @@ -1647,47 +1647,3 @@ The coalescer could coalesce "edx" with "eax" to avoid the movl in LBB1_2 if it commuted the addl in LBB1_1. //===---------------------------------------------------------------------===// - -These two functions perform identical operations: - -define i32 @test(i32 %f12) { - %tmp7.25 = lshr i32 %f12, 16 - %tmp7.26 = trunc i32 %tmp7.25 to i8 - %tmp78.2 = sext i8 %tmp7.26 to i32 - ret i32 %tmp78.2 -} - -define i32 @test2(i32 %f12) { - %f11 = shl i32 %f12, 8 - %tmp7.25 = ashr i32 %f11, 24 - ret i32 %tmp7.25 -} - -but the first compiles into significantly better code on x86-32: - -_test: - movsbl 6(%esp), %eax - ret -_test2: - movl 4(%esp), %eax - shll $8, %eax - sarl $24, %eax - ret - -and on x86-64: - -_test: - shrl $16, %edi - movsbl %dil, %eax - ret -_test2: - shll $8, %edi - movl %edi, %eax - sarl $24, %eax - ret - -I would like instcombine to canonicalize the first into the second (since it is -shorter and doesn't involve type width changes) but the x86 backend needs to do -the right thing with the later sequence first. - -//===---------------------------------------------------------------------===// |