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llvm-project/llvm/test/CodeGen/SPARC/stack-align.ll

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[Sparc] Support user-specified stack object overalignment. Note: I do not implement a base pointer, so it's still impossible to have dynamic realignment AND dynamic alloca in the same function. This also moves the code for determining the frame index reference into getFrameIndexReference, where it belongs, instead of inline in eliminateFrameIndex. [Begin long-winded screed] Now, stack realignment for Sparc is actually a silly thing to support, because the Sparc ABI has no need for it -- unlike the situation on x86, the stack is ALWAYS aligned to the required alignment for the CPU instructions: 8 bytes on sparcv8, and 16 bytes on sparcv9. However, LLVM unfortunately implements user-specified overalignment using stack realignment support, so for now, I'm going to go along with that tradition. GCC instead treats objects which have alignment specification greater than the maximum CPU-required alignment for the target as a separate block of stack memory, with their own virtual base pointer (which gets aligned). Doing it that way avoids needing to implement per-target support for stack realignment, except for the targets which *actually* have an ABI-specified stack alignment which is too small for the CPU's requirements. Further unfortunately in LLVM, the default canRealignStack for all targets effectively returns true, despite that implementing that is something a target needs to do specifically. So, the previous behavior on Sparc was to silently ignore the user's specified stack alignment. Ugh. Yet MORE unfortunate, if a target actually does return false from canRealignStack, that also causes the user-specified alignment to be *silently ignored*, rather than emitting an error. (I started looking into fixing that last, but it broke a bunch of tests, because LLVM actually *depends* on having it silently ignored: some architectures (e.g. non-linux i386) have smaller stack alignment than spilled-register alignment. But, the fact that a register needs spilling is not known until within the register allocator. And by that point, the decision to not reserve the frame pointer has been frozen in place. And without a frame pointer, stack realignment is not possible. So, canRealignStack() returns false, and needsStackRealignment() then returns false, assuming everyone can just go on their merry way assuming the alignment requirements were probably just suggestions after-all. Sigh...) Differential Revision: http://reviews.llvm.org/D12208 llvm-svn: 245668
2015-08-21 12:17:56 +08:00
; RUN: llc -march=sparc < %s | FileCheck %s
declare void @stack_realign_helper(i32 %a, i32* %b)
@foo = global i32 1
;; This is a function where we have a local variable of 64-byte
;; alignment. We want to see that the stack is aligned (the initial
;; andn), that the local var is accessed via stack pointer (to %o0), and that
;; the argument is accessed via frame pointer not stack pointer (to %o1).
;; CHECK-LABEL: stack_realign:
;; CHECK: andn %sp, 63, %sp
;; CHECK-NEXT: ld [%fp+92], %o0
;; CHECK-NEXT: call stack_realign_helper
[SPARC] Fix stupid oversight in stack realignment support. If you're going to realign %sp to get object alignment properly (which the code does), and stack offsets and alignments are calculated going down from %fp (which they are), then the total stack size had better be a multiple of the alignment. LLVM did indeed ensure that. And then, after aligning, the sparc frame code added 96 (for sparcv8) to the frame size, making any requested alignment of 64-bytes or higher *guaranteed* to be misaligned. The test case added with r245668 even tests this exact scenario, and asserted the incorrect behavior, which I somehow failed to notice. D'oh. This change fixes the frame lowering code to align the stack size *after* adding the spill area, instead. Differential Revision: http://reviews.llvm.org/D12349 llvm-svn: 246042
2015-08-27 01:57:51 +08:00
;; CHECK-NEXT: add %sp, 128, %o1
[Sparc] Support user-specified stack object overalignment. Note: I do not implement a base pointer, so it's still impossible to have dynamic realignment AND dynamic alloca in the same function. This also moves the code for determining the frame index reference into getFrameIndexReference, where it belongs, instead of inline in eliminateFrameIndex. [Begin long-winded screed] Now, stack realignment for Sparc is actually a silly thing to support, because the Sparc ABI has no need for it -- unlike the situation on x86, the stack is ALWAYS aligned to the required alignment for the CPU instructions: 8 bytes on sparcv8, and 16 bytes on sparcv9. However, LLVM unfortunately implements user-specified overalignment using stack realignment support, so for now, I'm going to go along with that tradition. GCC instead treats objects which have alignment specification greater than the maximum CPU-required alignment for the target as a separate block of stack memory, with their own virtual base pointer (which gets aligned). Doing it that way avoids needing to implement per-target support for stack realignment, except for the targets which *actually* have an ABI-specified stack alignment which is too small for the CPU's requirements. Further unfortunately in LLVM, the default canRealignStack for all targets effectively returns true, despite that implementing that is something a target needs to do specifically. So, the previous behavior on Sparc was to silently ignore the user's specified stack alignment. Ugh. Yet MORE unfortunate, if a target actually does return false from canRealignStack, that also causes the user-specified alignment to be *silently ignored*, rather than emitting an error. (I started looking into fixing that last, but it broke a bunch of tests, because LLVM actually *depends* on having it silently ignored: some architectures (e.g. non-linux i386) have smaller stack alignment than spilled-register alignment. But, the fact that a register needs spilling is not known until within the register allocator. And by that point, the decision to not reserve the frame pointer has been frozen in place. And without a frame pointer, stack realignment is not possible. So, canRealignStack() returns false, and needsStackRealignment() then returns false, assuming everyone can just go on their merry way assuming the alignment requirements were probably just suggestions after-all. Sigh...) Differential Revision: http://reviews.llvm.org/D12208 llvm-svn: 245668
2015-08-21 12:17:56 +08:00
define void @stack_realign(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g) {
entry:
%aligned = alloca i32, align 64
call void @stack_realign_helper(i32 %g, i32* %aligned)
ret void
}