[clang] [lld] [llvm] [LLVM][WebAssembly] Implement branch hinting proposal (PR #146230)

[Lukas Döllerer via llvm-commits]

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@@ -0,0 +1,79 @@
+; RUN: llc -mcpu=mvp -filetype=obj %s -mattr=+branch-hinting -wasm-branch-prob-high=0x60000000 -wasm-branch-prob-low=0x0 -o - | obj2yaml | FileCheck %s
+
+; This test checks that branch weight metadata (!prof) is correctly translated to webassembly branch hints
+; We set the prob-thresholds so that "likely" branches are only emitted if prob > 75% and "unlikely" branches
+; if prob <= 0%.
+
+; CHECK:        - Type:            CUSTOM
+; CHECK-NEXT:     Relocations:
+; CHECK-NEXT:       - Type:            R_WASM_FUNCTION_INDEX_LEB
+; CHECK-NEXT:         Index:           0
+; CHECK-NEXT:         Offset:          0x5
+; CHECK-NEXT:       - Type:            R_WASM_FUNCTION_INDEX_LEB
+; CHECK-NEXT:         Index:           2
+; CHECK-NEXT:         Offset:          0xE
+; CHECK-NEXT:     Name:            metadata.code.branch_hint
+; CHECK-NEXT:     Payload:         '8380808000808080800001050101828080800001050100'
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Lukasdoe wrote:

Very good idea, I just did not think about that option. Implemented yaml parsing for branch hints now anyways, so we now test both representations.

https://github.com/llvm/llvm-project/pull/146230