[WIP] from Souper IR to WASM (#13)

* basic solution for souper2wasm

* minor improvements

utils/souper2wasm/README.md

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+# from Souper IR to WASM
+
+__Souper IR → LLVM IR__
+Souper's [souper-check.cpp](https://github.com/google/souper/blob/master/tools/souper-check.cpp) and [souper2llvm.in](https://github.com/google/souper/blob/master/utils/souper2llvm.in)
+
+__LLVM IR → WASM__
+`llc -mtriple=wasm32-unknown-unknown` ([blog](https://medium.com/@richardanaya/write-web-assembly-with-llvm-fbee788b2817))
+
+## run demo
+```
+zsh run.sh
+```
+
+## requirements
+Python >= 3.6
+LLVM >= 8.0
+
+## existing issues
+- In some cases (like `demo/negate.opt`), width info can not be identified correctly

utils/souper2wasm/demo/infer.ll

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+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+
+define i1 @foo(i1 %x1, i64 %x2) {
+entry:
+  %0 = icmp ult i64 135637824071393761, %x2
+  %1 = or i1 %x1, %0
+  %2 = select i1 %1, i64 135637824071393761, i64 %x2
+  %3 = icmp ult i64 135637824071393761, %2
+  ret i1 %3
+}

utils/souper2wasm/demo/infer.opt

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+; REQUIRES: solver
+
+; RUN: %souper-check %solver -infer-rhs -print-replacement %s > %t1
+; RUN: %FileCheck %s -check-prefix=SUCCESS < %t1
+; RUN: %parser-test < %t1
+; RUN: %souper-check %solver < %t1 | %FileCheck -check-prefix=LGTM %s
+; RUN: %souper-check %solver -infer-rhs %s > %t2
+; RUN: cat %s %t2 | %souper-check %solver | %FileCheck -check-prefix=LGTM %s
+
+; SUCCESS: RHS inferred successfully
+; LGTM: LGTM
+
+%0:i1 = var
+%1:i64 = var
+%2:i1 = ult 135637824071393761:i64, %1
+%3:i1 = or %0, %2
+%4:i64 = select %3, 135637824071393761:i64, %1
+%5:i1 = ult 135637824071393761:i64, %4
+infer %5
+

utils/souper2wasm/demo/negate.opt

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+; REQUIRES: solver
+
+; RUN: %souper-check %solver -print-replacement %s > %t1
+; RUN: %FileCheck %s < %t1
+; RUN: %parser-test < %t1
+; RUN: %souper-check %solver %t1 | %FileCheck %s
+
+; RUN: %souper-check %solver -print-replacement-split %s > %t2
+; RUN: %FileCheck %s < %t2
+; RUN: %parser-test < %t2
+; RUN: %souper-check %solver %t2 | %FileCheck %s
+
+; CHECK: LGTM
+
+%0:i64 = var
+%1:i64 = xor %0, -1:i64
+%2:i64 = add %1, 1:i64
+%3:i64 = sub 0:i64, %0
+cand %2 %3

utils/souper2wasm/run.sh

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+echo "py ... \c"
+python3 souper2llvm.py demo/infer.opt
+echo "okay"
+
+echo "llc ... \c"
+llc -mtriple=wasm32-unknown-unknown -O3 -filetype=obj demo/infer.ll -o demo/infer.o
+echo "okay"