[llvm] [AMDGPU] getMaxLocalMemSizeWithWaveCount: Align to LDS granularity (PR #219172)

[Lucas Ramirez via llvm-commits]

================
@@ -0,0 +1,37 @@
+; RUN: opt -S -mtriple=amdgpu9.50-amd-amdhsa -passes=amdgpu-promote-alloca -disable-promote-alloca-to-vector < %s | FileCheck %s
+
+ at lds_12800 = internal addrspace(3) global [12800 x i8] poison, align 16
+attributes #0 = { "amdgpu-flat-work-group-size"="64,64" }
+
+; This is a regression test for a bug in getMaxLocalMemSizeWithWaveCount
+; which did not round to the LDS allocation block size, leading
+; AMDGPUPromoteAlloca pass to overestimate the available LDS.
+
+; We have LocalMemorySize = 163840, allowing for floor(163840/ 12800)
+; = 12 workgroups and occupancy 12 / 4 = 3 with the 12800 bytes of LDS
+; usage and one wave per workgroup.
+
+; Without aligning down to the LDS granularity of 1280 in
+; getMaxLocalMemSizeWithWaveCount, the limit in alloca promotion is
+; 163840 / 12 = 13653 bytes which led to the promotion of the alloca
+; in the function.
+
+; With rounding down, the promotion limit is 12800 bytes. The alloca
+; would add 64 * 10 bytes which exceeds the promotion limit.
+; This prevents the promotion of the alloca.
+
+; CHECK-LABEL: @test(
+; CHECK: %stack = alloca [10 x i8], align 1, addrspace(5)
+
+define amdgpu_kernel void @test(ptr addrspace(1) %out, i32 %idx) #0 {
+
+  %stack = alloca [10 x i8], align 1, addrspace(5)
+  %lds.ptr = getelementptr inbounds [12800 x i8], ptr addrspace(3) @lds_12800, i32 0, i32 0
+  store volatile i8 1, ptr addrspace(3) %lds.ptr, align 1
+
+  %arrayidx = getelementptr inbounds [10 x i8], ptr addrspace(5) %stack, i32 0, i32 %idx
+  store i8 7, ptr addrspace(5) %arrayidx, align 1
+  %load = load i8, ptr addrspace(5) %arrayidx, align 1
+  store i8 %load, ptr addrspace(1) %out, align 1
+  ret void
+}
----------------
lucas-rami wrote:

missing newline at EOF

https://github.com/llvm/llvm-project/pull/219172